I'm not really a big fan of the mechanical aspect of Obligation, especially compared with Duty.

My group has six players and, since Obligation can never drop below 5, that means that we'll likely go several sessions where we're almost certain to trigger someone's Obligation and reduce everyone's ST. Even if we all do somehow manage to reduce our Obligations to 5 apiece, we're still looking at a 30% chance to trigger.

Meanwhile, triggering Duty grants a boon to the group when triggered and an even bigger boon when the group gets their collective Duty to 100.

It just seems like Obligation is designed to punish players into roleplaying instead of entice them to.