Unlimited subs? Is that it?
First of all, subs aren't unlimited. Compared to youth club play, they are very limited.
Secondly, having the ability to move players in and out of a game allows the coaches to be more creative in their development techniques. If not subbing were important, the coach is free to do that and even advertise it as a benefit good players would see in his program.
Be thankful we do not go back to the old days in which FIFA permitted no subs - someone got hurt, you played short. The trend over they ears has been to make FIFA rules more like NCAA. We can only hope.