If it's at a sit-down restaurant and I'm with friends, I'm fine with slow service, provided I'm not with my friends that constantly **** when they are hungry. A good meal is worth slow service every now and then. If the service is bad as in they keep messing up orders and are rude, then I would say it isn't worth it.
If I'm by myself and just hungry and poor, I'm perfectly fine with passable food, especially if it's quick and cheap.