The best way to think of bound spirits, is as contract employees.
They only do things that they get paid for... and they are paid in "services"....
Or, another way to look at it is: Your boss comes to you on Friday afternoon and says "need you to put in 10 hours on Saturday AND Sunday. Oh and I'm not paying you either." What do you say back?
(Personally, I laughed in his face. Full on belly laughs for about 5 straight minutes, before saying "Hell No. See you Monday")