All I've gotten from info I've read up on is that you press the SMART button and look under to slide or over to climb/vault. From other things I've gotten is that jumping before using the SMART button makes certain things faster. If you could give me a link where it says that you can manually do things SMART does (ie. Mirrors Edge) than that would be great. :turned:
So far they seem to have been pretty clear that all SMART does is automate the jumps and slides to get you from A to B without having to bother doing it yourself. Run up to a wall while holding smart, it will climb and mantle over it once you get there, yet you can do it on your own using the jump button (I assume). Run up to a railing while looking down and SMART will automatically slide under, yet there's nothing preventing you from simply pressing the slide button manually.
In fact, it's also been mentioned that SMART isn't optimal, as you said. If won't jump to the wall to minimize time required to mantle over it, but wait until you get there before climbing; nor will it be able to wall-jump to reach higher ledges, which will have to be done manually.
However, some maneuvers might be extremely hard to achieve without the use of the SMART button. Just look at the http://brinkthegame.com/features/freedom/ video, especially the part going from 0:29 to 0:38. SMART figures you're trying to cross over to the other side and thus jumps slightly to the left and right to land on the available ledges; although possible, timing those jumps perfectly might be something few can achieve every single time, and the use of SMART in that situation might prove helpful even to the best players.