Benefits from being in a team include
Dressing room
Two quests: Point of Disaster which is ran somewhat frequently and robots reckoning which is not
And you have people you can play with at any time.
Plus you have their banner beside your name
well ultima has happy hour which destroys prices of just about anything with 200% drop rate
This is just 25% but it would take a long time to actually get the 25% as well