I think you'll find at many places you're earning future consideration as well as current comps. If you prove yourself a good player you'll receive invitations to come back in the future for free or reduced rates. These will be the same based on your level of play and won't change based on whether you were given a comped dinner on your last visit or not. I know when you have the "RFB" after your name it definitely makes a casino visit more fun!