I wouldnt want to get attached to a Young player because he will be hard to let go. Plus I never keep players I don't need. If your not producing the way I want or your skills drop your gone, period. My goal is to build my arena and keep my team winning. train players takes away from working on game shape. I rather start training when my team is well established (D2 or above). Who knows my theory might not work but I'm 35-7 overall so it's working for now. As long as I can keep a winning record I'm str8. Only fix something when you see it's broken right?
The problem is, you can't *start* training in D II. Well, not and stay in D II at least.
And training players doesn't take away from working on game shape, especially since you shouldn't have to "work" on game shape.
Most importantly, though, you don't have to necessarily let the young players go either. What you can always do, for example, is train five young guards for four or five seasons with two position training (which also means they need lower potential and therefore cost less), and then a group of big men for a few seasons, and you've suddenly got a team that is improving each season and outperforming their salary, plus they'll be custom built by you to play however you want them to. As you start moving up, you can switch to better potential players (I went to better bigs after my guards), and of course at higher levels you'll need to supplement that core with higher quality starters.