At that time, common people like you and me will panic and change in big amount. Causing the RM to slide further. Somehow damage control need to be done to prevent situation from worsening.
Imagine, money is dropping lower everyday at a rapid rate (like in Venezuela) You don't change your money, your money keep dropping lower everyday at a fast rate.Your only option that time, change to other stronger currency/change to gold.

Good eg was 1997/98 time. Public panic and change in big amount. Had BNM didn't impose capital control that time, situation would have been worse.

Take china. China is one perfect example of capital control at the moment. Their citizen keep charging money/finding creative way to bring money overseas to escape the yuan depreciation. Had china don't impose capital control, the yuan would have continue sliding.

From what I read in the 1998 incident, no one can bring money out of the country without valid reason. Money from overseas which was already in maalysia cannot be taken out from Malaysia for 3 years.

Now, china do capital control where their citizen can only transfer/change max USD50k/year.

Even indon tax amnesty is also some kind of capital control as money bought back to the country cannot be allowed to leave indon for I think 2 years.

All this is done to prevent money flowing out of the country thus sustaining the local economy. When we change money/transfer money out/shop from overseas/invest in overseas market, we are actually causing the RM to flow out. Same can be said about those illegal/foreign workers who repatriated billions of money out of the country yearly.

Right now there's no capital control. Right now we only have BNM NDF which means companies can only use BNM price for foreign currency transaction. Not so liquid. Is some kind of control. Previously companies use market price for their foreign currency transaction.

How MNC do it? They park their money overseas in countries without the need to bring the money into malaysia unless needed. They can also hedge the currency so in case the currency swing mot in their favour, they won't be affected by it. Don't ask me how hedging works. I don't know how you can hedge the currency. Now with new BNM ruling where all companies doing export businesses need to bring their money back to malaysia. 75% must be converted back to Rm via onshore banks. 25% can be foreign currency which must be in onshore banks. So in some way, exporters are force to bring money back. It's some kind of control. You don't like this ruling, don't set up shop in malaysia.

How can they control it? They can go the china way where they limit citizen to max USD50k/year. Limit how much you can spend overseas with your credit card. They also clamp down on bitcoins. Thus china citizen cannot buy bitcoins which means they cannot transfer the money out of china.

Or they can do it the Argentina way. Preventing citizen from doing online shopping with by making them pay 50% of tax for all foreign items shipped in. Preventing them from changing money/transfering money overseas.That's why Argentina are turning to bitcoins. It's not regulated which means the argentina govt can't control the citizen from transfering the money out. Why didn't argentina block bitcoins? My guess is they are not as advance as china.

Country can limit how much a citizen is allowed to transfer the money out and how much they are allowed to change (as demonstrated by china). We haven't reached that stage yet. But we reached it before in 1998.

That's why you must declare the purpose and must give proof. Failing to do so, can cause the banks to reject your transfer. This we have. Not sure if it's to limit how much you can transfer out/for anti-money laundering purpose. Banks said it's for anti money laundering purpose.

For malaysian, as long as we have no loans/debts, we are free to transfer how much we want. If you have some kinf of loan/debts, max one is allowed to transferred out per year is RM1M for now. If RM depreciate at an alarming rate, BNM can impose rules like china and say maybe limit us to max RM50k/year of foreign currency transaction. Not sure what's the 1998 level which was enforced on malaysians.
That's why, if you are worried about capital control, keep some money overseas. Overseas money are out of reached of the central bank. They cannot stop that money except for central bank of the country where money is kept. Exception to this rule is US. US govt have far reaching arms. That's why some americans renounced their citizenship because they don't like that the govt can have access to their money even though it's overseas. American passport is actually a curse as no country banking system will want to do anything with an american customer due to far reaching arm of US govt.

Eg. If you intend to send your kids overseas, park your money where you want to send your child too. In the event of capital control, your kid still can continue with his education with the money you park overseas although you cannot send any money out of the country. Your kid won't suddenly be kick out of the uni for not making payment.

You may consider bitcoins too if you are worried about capital control. Bitcoinis the only thing to protect from capital control anywhere in the world. As long as there's a bitcoin exchange in some part of the world, they are willing to exchange your bitcoins with money. Why not gold? You can't carry much gold overseas. If you tried carrying USD1m worth of gold overseas, definitely you will br stop by customs. But carrying USD1m worth of bitcoins, no problem as all you need is a username and password

Just to give you another perspective contrary from the pessimistic view of bro ramjade that seems to imply capital control is on the BNM's discussion table now

Capital control is the very last resort a country would take. In the AFC in 1998, Mahathir was forced to impose capital control to stabilise the currency attack by George Soros (purportedly). Malaysia's currency reserves was very low at that time, so he has not much choice to fight Soros. The reserve level is different now so it is way more risky for a speculator to repeat the same thing and be successful like AFC.

During capital control at that time, business (import and export) are still on going. It doesn't mean no inflow or outflow of forex during that period. Just that BNM required the banks for stricter documentation. In fact, after the peg of 3.80, all import and export businesses got a relief and resume businesses with more certainty. So, capital control doesn't mean a stop to forex transfer. It just means for business, more documentation has to be provided to the banks for scrutiny. If capital control means no forex movement, then you cannot buy stuff like BMW, Iphone, grapes/apples, Hollywood movies, petrol for our cars and what not. Exporter cannot sell their good overseas...It is a big misconception capital control means no forex transfer.

For individual, same applies. Eg. Money used for education were still allowed. Like businesses also, the banks required strict documentations from individuals. So, necessary personal expenses were permitted during that time

Investment activities will be curbed though. Just like in 1998, share market trading activities, investment money in and out of the country are restricted (not banned, but need strict review and approval by BNM)

Reading bro ramjade's comment, it seems to me that capital control is a possibility now. Not saying it is impossible, but If you feel it is a possibility, then increase in GST would most probably precede capital control. Instead of the rhetoric in Ramjade's comment, you should see signs and numbers in deterioration of GDP growth, inflation, unemployment, debt level, Malaysia' current account turns deficit, interest rate hike at unusual quantum, the big 3 international rating agencies downgrading Malaysia's economic position....all these signs will give you some warning before BNM take the drastic and emergency action on capital control.

I think Hudud law be implemented and opposition wins the next GE is more likely to happen than BNM imposing capital control 

Implementing capital control is like a doctor using defibrillator on a person whose heart stops beating. It is the only last hope trying to revive the crisis

hi you guys~think waiting till 3.8 USD rate, i will change for 500~1000USD for keep. After election i think the MYR will start going weak.

I have put my RM overseas for years. It's never too late to start. Start with the mindset that mine his one way ticket and you won't see it for at least minimum 10 years.

I hold SGD, GBP, USD and CAD inside IBKR.