I think the most useful answer to that comes from a discussion about concerns and problems either might have. Each relationship has its own dynamic, and trying to determine a universal rule of thumb seems self-defeating.
Though I suppose I expect people to do what they want to do for me (i.e. not you scratch my back and I'll scratch yours) and to talk to me about it if they feel something's gone sour. Unless it's not very deep, in which case I expect we'd grow apart.