They get paid shitloads and they virtually do nothing. Alot do more bad than good, so when somebody is normal (e.g Sheens putting up with Benji playing like a retard half the time because that's his 'natural' game whereas Bennett would tell him to play normal and not put up with his shit) he's the best coach of all time.
Depends on their role within the club as a whole really. Rick Stone for instance was essentially just barely above being considered a head trainer, while someone like Des Hasler seemed to be heavily involved in absolutely everything at Manly.
Tim Sheens has down syndrome and probably the most talented roster in the NRL is sitting second last on the table as a result. Craig Bellamy has a team who admittedly has 3 of the best players in the game, but at the same time is able to get his team up for every single match at peak performance and able to turn average players into stars and has his team at the top of the table.
