From economic standpoint , calcium also good enough right

it is good for moving & sliding parts which expose to weather.
just dont apply it to bearing.

In layman term, calcium grease is also called heavy grease or chassis grease if u r get them in workshop or local hardware shop.

It is safe on rubber or bushes as well right. Coz i have seen ppl putting on bushing

to be safe, no!
silicone grease (or oil) is the right choice to buff your rubber and plastic part, not calcium grease.

Ok bro. Then y not just use silicone on hinges n so on as well

can. make sure the silicone is solvent base and not water base.

how about the keyholes for motorcycle tank...once it got jammed and i just sprayed wd40 in... problem solved...
but..is it advisable?

keyhole must stay dry all time. oil is not appropriate. use only moly or graphite powder.
end user will have problem aquiring industrial grade moly powder, so my advise is to scrape off the carbon tip from the pencil using a pen knife, make sure it is in fine talcum form.

Put the powder into the keyhole and apply thin layer onto the key too.

Note. not too much powder into keyhole u dont wanna fill it.

But in your opinion is it advisable to spray WD-40 into the keyhole? Any disadvantage or is it a good practice?

I also do it from time to time but not sure if it does any lasting damage..

This is the trick that paint shop using

https://www.youtube.com/watch?v=xL2HIuJR43A

simply no.

1. an oily and greasy keyhole attracts dust and particles making it more prone to jamming the key in future.
2. oil in the keyhole will stained your key, u dont want an oily key in your pocket. an oily key also attacts dust which back to point 1.

technically the oil doesnt kill the lock, but the dirt does.

ok..

1. a keyhole by its nature isn't open to natural ventilation thus attracts dust and particles except via the act of inserting the key itself..
WD-40 is more a penetration liquid and hygroscopic removing oil,dust and moisture and evaporating leaving a non oily residue (from what i understand)

2. Thus the buildup of oil due to WD-40 becomes a non-issue, with it the attraction of dust and other sticky contaminants..

If the above is true then the only issue would be the removal of the natural lubrication oil within the keyhole itself that is a worry..

Appreciate your further thoughts..

What about using silicone spray for general car lubrication of joints n so on