the negative point in training a player for skills he does not need is that the wages go up.
On the other hand there is no such thing as an unneeded skill. Unlike in hattrick the players here use ALL their skills at a given time.
It is clearly said in the rules that shot blocking is not very usefull for guards...however, my guard blocked 2 shots in 1 game one time, so he did use his skill, he just does not use it often, maybe even seldom, but he uses it.
on the other hand my center does quite often fire away from 3point range, if my opponent defends man to man, mostly his center is defending mine, so his center will use his outside D as well...
You could discuss that you only want to pay for the skills the players use more than 50% of their time, or you could prefer to have every possible skill as high up as possible and gladly pay for it. It's everyone's own call I think, and probably both are favored by numerous people, so whatever you choose yourself, there will always be people who think like you. ;)
They are not your friends; they dispise you. I am the only one you can count on. Trust me.