I play as a very "hands on" manager and control both my Reserves and Youth teams and have found it very beneficial to do so. I have had a good number of successes where youth players appears to be underated by my assistants and would never have been given a contract had I not intervened. By controlling how they play, and with the right training I have significantly improved the worth of some players that otherwise would have been overlooked. Promising Youth players get moved to the Reserves where I can then apply further polish to get them ready for first team games. At the very least I've drastically increased their value if I then decide to sell them off. The bulk of my transfer income comes from players I have nurtured but don't feel are quite good enough or just don't have room for in thier postion in the first team. so far this season I have made 17 million selling such players. I doubt I would have made anywhere near that had I not nurtured them as I did. Players deemed not to have much potential are typically hard to shift and would otherwise have been realeased for free.
Controlling Reserve games I also find useful for a number of other reasons, such trying out new tactics, retraining players into different postions or giving players (particularly strikers) who've hit a bad patch their confidence back again.