Main purpose should be getting help and some support from more expierenced players (or players with the same interests).
You have to do the gang actions. Some of them bring some bonus for you and don't harm you, some of them can hurt (like fight against Gang of Shadows, but this can be integrated in your kind of play).
You should gain some nice, private atmosphere (in chat or direct mail) with your gang members. So it is higly recommended to talk to the inviting gang about duties and aims.
