When to self-manage your HOA vs. hiring a property manager?

I am wondering about the decision to self-manage versus hiring a property manager. Is there a certain size condo association that self-management does not make sense? My experience is that smaller properties (3-10 units) can self-manage no problem and hiring a property manager is not necessary. I have also see much larger associations (~100+ units) that I would expect to hire a prop mgr self-manage. I am interested to hear others perspective and experience on the matter.