I can't tell you how many times I've had to cover for people and then get shafted when i needed coverage. It's because once you end up becoming a “really good employee” they look at you different. They see you as more important to have on your staff and while that can be a good thing it has its negatives. Nothing is worse than during the same day get asked to work again into the night. Or when you have to do a double knowing you have a dreaded morning shift the next day that they “need you” for.