Youth players that you get are normally a 4* (but sometimes 3*) which costs between 12-24T and they are fast trainers and you have to use green boosters to develop these players to a decent standard for your team and you can train them extra roles and SA if required. The other youth is a 2* (or 1*) duck which can be sold for quick $ since they will never really be good enough to play for your team.

Another major problem is the timing of the youth players arrival and they can arrive late in the season and lose a star should your team promote to the next level making them less attractive to buy.