One of the biggest assets that guilds have is that they allow players to pool their resources so that everyone can benefit. This is also one of the biggest drawbacks because it raises a whole mess of additional issues.
Pooling resources is, let’s be honest, a good thing. It means that players who are unlucky with random rewards can catch up, players who have more than they need can share with others, and everyone in the guild feels as if they’re more or less on a level playing field. At the same time, it also means that you have to tacitly acknowledge at first that the players are not starting on a level playing field, and by pooling resources at times you can wind up with less of a leveling effect and more of a selfish roommate situation.