If this means stamina - yes, players perform much better when on 9 or 10. It is usually best, if you train your players "normal" skills for as long as you need (NT caliber players until 28-30, superstar potential players more until 25, etc.), then you complete them with stamina (and free throw if you don't have training court) training. During training it is probably only worth if you have very low (1-2) stamina.
Stamina can easily be worth two levels of each skill if you compare level 1 to level 9.