>>724781964
If you are doing the main story to credits, you don't need to and actively should not engage with every mechanic. Engage with the mechanics that are fun to you. Do you have a unit you like and did you see an Evility that you think would have synergy with that? Then do that. Want to push your characters item level a bit to buff up the raw damage? Go for it. The charm of Disgaea is that you can make units your own and run whatever you want.

You only need to care about things like Innocents and making use of every mechanic when you enter the post-game where the goal is to become comically OP by putting everything together.