Complain - if something wasn't right - tell them.

If it was really bad you may get something free out of it but management should know when things are affecting their service. You are doing the business a good service by complaining about SOME things. If a manager does not know, they can't fix the situation and it will continue to happen. If there is something wrong with a product, it will stay on the shelves and not sell as people begin to find out but it can't be corrected until someone says something. You may get a refund of the purchase price. You may get an entirely free meal. You may get coupons for your next visit. You may not get anything but you've helped your world. Most importantly in the complaining, be as polite and courteous as possible - that usually helps with getting a bonus in return. :D