Just started spring training in my world. Was wondering if it's better to play the younger players with potential ONLY, as opposed to playing my ML projected season starting lineups..some of these ML players are in their 30s with no more potential growth....not sure how to go about this.

You should get plenty of different responses but here's what I do:

I give my vets 10 AB(position players) or 3 appearances(all as RP).
I give my 2nd level prospects the same.
Then I give my real prospects TONS of PT.

I like 25 at bats for everyone that matters (BL players and prospects I feel will make the majors) there is enough to go around if you plan it right.

For pitchers, I like 5 appearances. Amount of innings is irrelevant to me. Just so long as they step on the mound.

I've heard people saying that giving vets spring training time prevents decline in ratings but I've yet to see proof for or against this.

I've not played vets and they have taken hits. Might have been natural, might have been not playing. I don't take that chance any more to find out.

If I have a deep team I try to get 3 guys in at every position per game but that only works when I'm winning in the 7th or later (player rest in the 4th inning plus defensive replacement in the 7th). For pitchers I'll use 5 or 10 max PC and spam as many appearances as I can get. Keeps players rested for regular season and gets as many games in as possible (assuming that's what counts towards ratings development rather than AB's or innings)

Also, I get a kick out of seeing box scores filled with 40 players from one team.

lol Ok cool, thanks guys