My wife and I have three children ages 6, 8, and 13. Our oldest is self-sufficient and can help if needed. We really just need the occasional sitter for when we want to go out.
We need a sitter to basically make sure the kids eat dinner and get ready for bed. Sitters in the past usually play or watch them until bed time, then just put on a movie for them to fall asleep to. Once the kids are asleep, you're free to watch tv, or whatever until we get home.
We usually just want a sitter for a night on the weekends.