You can make an argument for this both ways. If you were to do it people would take scouting and draft more serious and possibly play this game longer. What I mean by this is they could buy some decent players to compete and also train guys for their future. Not have to pretty much choose one or the other. Lets face it, If you have three trainees chances are you have to play at least one as a reserve in real matches. Also when you want to train out of position highly likely to lose against a team with decent players.
On the other hand I can also see coaches using this to train great players just to sell (such as higher league players). This will flood the tranfer list and bring down the value of those players and make it really easy for anyone to purchase. That would cause lots of teams to go bankrupt as it may be cheap to buy them it is not cheap to pay them and this would hurt many new owners.
Those are just a few of the things I can think of for right now.