Auto-Distributor is okay, but it does evenly give each of the 3 categories the same amount of points, If you trained a player for 30 skill points, hitting auto-distribute would most likely assign 10 to defence, 10 to attack, 10 to physical or mental. Assigning them yourself could make a player over powered on of the 3 areas.
I have a striker, Def 90.4, Attack 105.4, Physical/mental 105.4... I don't know whether that striker would perform better than a striker that had Def 100.4, Attack 100.4, Physical 100.4 both strikers would have the same amount of quality, but I don't know if weighting a player to 1 or 2 of the 3 categories would give better performances, I have had evenly distributed points on players and they perform just the same.