I'm in Div V currently, and thus have a bit of freedom in playing players out of position in order to get my young fellas their training minutes in specific positions. Even so, it is difficult to train 6 players when doing two position training due to them fouling out sometimes. I can just imagine that in higher leagues if you want to be competitive you have to play your best players (playing a rookie SF for 48 minutes in a Div III league game would get you crushed), and also allow for subs so your players don't get too tired and cause you to lose. It seems this would mean you have to sacrifice training your prospects to the max in order to stay in the playoff race, and instead rely mainly on scrimmages to train your players.
Does that sound about right?