As always, it is a trade off. I had gameplans setup to play all the young guys in blow outs and less important games and saw small WE increase across pretty much everyone on the team will only a few losing WE. The younger guys got a bit of a growth boost and the starters didn't grow as much compared to having the starters just play.
My take is that if the starter is a SR, then it is worth the effort to fiddle with the gameplan to get a growth headstart for the younger guys, but if the starter is a Jr or younger, I would let them play as much as possible to keep him growing. I would also factor in their potential and projected end rating based on WE, Starts, playing time and potential to make the decision.
Having said all that, I haven't had time to actually implement that model on my current teams