They only do it to make the runners who get done early call in if they want their 8. For everyone else who's working 12 hour days it makes no difference. Though if they just up and change it without letting people know (ie they have been fine paying runners their 8 when they get done early, but then change the paid code without telling them) that's pretty shady. I always ask for my 8 if I'm getting done early so I never look to see how I'm coded.