There are times when you're forced to rely on MP burst if you're trying to keep someone up that's being focused from a hard switch, especially in ranked arenas and even sometimes in wzs/arenas.
True, there's a standard rotation for everything, but desperate times calls for desperate measures when just a simple kolto bomb or hammer shot isn't going to do it especially when you don't have BI, tech override, or any CC available after casting MP.
If you're desperately trying to keep someone alive under extreme pressure, you will go down below 75% ammo, I guarantee it. Sometimes, under extreme circumstances, the standard rotation(s) isn't going to work.