It makes no sense to me that a gamemaker would create a "useless" rating or that they'd opt to invert 1 rating to lessen confusion (if IRC, from a CS response).  I'd imagine that a player's temperament in conjunction with the way they're being disciplined, the patience of the player and coach along with the coach's strategy and player's makeup all contribute somehow (length? rate?) to the "standard" development process.

Though not useless (IMO), it is certainly secondary to the ratings that dictate performance.  I usually only use it as a tiebreaker when ranking seemingly even draft prospects.  To a lesser extent I also try to pair my better prospects that have a Carlos Zambrano-like temper (whether that is 0 or 100) with coaches that have higher patience/discipline.