Originally Posted by
DaveSSS
If you know what reach and stack you need, then the only problem that can occur is finding out that you can't get a post that put's the saddle where you want it.
Quite true... but it isn't necessarily trivial. Sort of like not being able to get a stem that works decently because Reach or Stack are wrong. So another term which represents "setback" of the frame... which might as well be STA, or something similar for TT bikes... should also be considered an essential frame dimension.