I had a mother of twins send them both three days a week when she was on her mat leave with her new baby. I didn't feel sorry for the girls, this lady obviously had a hard time handling the two she already had (well paid professional woman by the way), so I felt happy for the girls that they got to come to me and play with their friends because they were likely getting more enjoyment/stimulation from their days with me.
I don't mind if parents spend their day off doing other things while their child is with me. I do, however require them to pick up by the time I know the latest kid will be leaving.
I also enjoy a day to myself to get things done, or go shopping alone, or even watch a movie!!! I am not just a mom and a daycare provider, but a person who has my own needs, as are these parents.