Having certain skill above 20 is useful although I wouldn't train it so much. But when such a player is on TL you don't bother whether he is a 21 or 19 in the skill. Of course having more skills at that level would make Cardenas from him, but kind of monoskill player can be useful and actually quite cheap (both TLwise and salarywise - they can be way cheaper than 100k actually). Role players to some extent of course.