According to Seven Stars Insider, you get the following if you opt out of maid service:

Harrah's Joliet - $5 in food and beverage credit per day.
Harrah's North Kansas City - $5 in food and beverage credit per day.
Harrah's Cherokee Casino Resort and Harrah's Cherokee Valley River Casino & Hotel - $20 in free play per day.
Harrah's New Orleans - 500 Reward Credits per night.
Bally's and Caesars Atlantic City, Harrah's Resort - $10 food and beverage credit per day.
All Las Vegas properties except The LINQ and The Cromwell - $10 food and beverage credit per day.

This is actually pretty good. I opt out of maid service anyway, because I don't like people in my room, and I am not so messy to where I need my room cleaned daily. (Do you get your house cleaned daily?)

You are still allowed to ask for extra towels, toiletries, etc.

Your stay must be at least 2 nights. If you stay only 1 night, this does not apply.

You must mention this at the front desk when you check in.