Wow, you guys are crazy. No offense man, but auto-weakness battle is the biggest "new" big ticket item that SMTIV brings to the SMT series and the genre as a whole. That's why the magazines were making a big deal about the new addition before the game was released.
It completely changes how SMT games are played. It's like a whole different game where there's no grinding, no grunt battles, only survival battles and boss fights. Just totally different pacing. I couldn't imagine playing SMTIV without it.
Once you hit a decent level (~10 or so), it's pretty much the must have application that you need. Playing without it, is like playing without auto-mapping.