If I remember correctly, you can carry quite a bit more people on your "roster" than the 10 that are going to be out in the field. This is meant so that if you call someone to play when a regular is not available, he is supposed to be on the original roster. This really only matters if another team protests you.

Pitchers are hard to come by. It's not as easy as it looks. I know a really good one, but he's not on IA. I'd rather someone from IA step up, but worse come to worse I have people available if need be.

First base is also pretty important.

Everyone can pretty much hit the ball, hence most games are won with good fielding since everyone will eventually hit the ball and score.