It's good to start out with a set of "rules" so that everybody knows what's expected of them. The problem, I think, is that many bands just sort of "form themselves" out of friends or session mates.   As they start working more and gigs are coming in each member naturally settles into what they are best at or inclined towards - and often that means one person ends up handling the business end of things, another the musical arranging, another the sound system, etc. Sometimes one person seems to get stuck with everything and the rest just seem to turn up, play their instruments or sing and pocket the cash, which they feel should be evenly divided.