In essence, the more you play a player, the faster he will progress towards his potential.
QBs are a whole different animal
I have had QBs with 90 potential and 100 pass accuracy potential that after their first camp had a 40ish current pass accuaracy.
It can take seasons for them to reach their potential but the more you play them the better. The problem is a low pass accuracy QB will really struggle until it approaches 60. So you have to weight the potential of a young QB versus the overall quality of the team. In some cases, letting a great potential QB sit and learn is best while other times it's better to play him and let the team takes its lumps.