Originally Posted by
dsbrantjr
A possible downside to locking out the M>L shift is that if you forget and force the shift you may jam the ratchet such that you cannot shift back down; you could even damage the mechanism.
Personally I would not consider going from 3x to 2x an upgrade but others might; I would miss those low range gears, and to get the same range out of 2 rings would necessarily spread out the remaining gears so the gaps would be bigger.
He said he's using the bike for cyclocross so on anything you'd need an ultra-low gear, you're probably better off dismounting and running up anyway. There aren't a lot of mile-long grinders on CX courses, just short steep pitches where you want to carry speed and muscle over it, if possible. Dismount and shoulder if not.