I know that players need playing time/innings pitched to develop, but does more or less matter? For instance, I have a top 5 pick who is a pitcher. Assuming I have the other pitchers on the team to do it, would it help to drop down to a 4 pitcher rotation for my prospect's team in order to get him in more games, or does it really matter? Would the extra work/innings be negligible?

If you're not going to let him pitch at less than 100%, he can only throw so many pitches.     If he can throw 80 in a 5 man, he'll throw throw 60 in a 4 man.

So in the end, no real benefit...

IMO, no.  Some think that appearances are more important.   I tend to disagree because, if that were the case, you should set all your true pitching prospects as SuA with a PC of 5/5.   Then they could get 100 appearances.

But, if you let SIMMY set your rotation, he puts the SP as SP.    That would be a contradiction. 

If you go by what SIMMY does, note that in rookie league he sets all pull ratings at 1... I would guess, to ensure that your prospects get their work in.

Given that game flow and bullpen settings affect whether a given pitcher even gets into games or not, I think the only way to ensure a pitcher gets X number of innings is to start with a spot in the rotation, max tolerable pitch count, and 1 pull rating.

I'm pretty sure I asked Mike a similar question in the past and Mike, you told me "set him to go as often as he can pitch at 100%", or similar.