Actually if SmartTag and TNG lanes are long, then you can use any of the Cash lanes for manual scanning. This is true with the Damansara toll, not sure about others, but I remembered reading that TNG can be used at all toll lanes, except SmartTag lanes.

In the evening, when exiting the Damansara toll, sometimes it is useless with SmartTag or TNG, easier to pass through with TNG on Cash lane and then squeeze yourself from the outer left lane.

My SmartTag cost me RM220 and been using daily since July 2001. I consider a good investment cos it saves me countless hours of time, petrol, and engine wear and tear.