As others have said, I've never been charged more for dine in. Glass vs plastic, bottomless drinks vs one trip are the only differences i've ever seen. It would never occur to me that I couldn't eat my to-go order in the restaurant, and I've done it before (ok, usually at very casual places) when I realize I have more time than I thought, or someone called and wanted to join me. It's not as if I'm bringing in my brown bag lunch to eat in their dining room; I paid for the food and the effort to prepare and hand it to me. I'm not getting table service, so I'm not taking up a server's time. The only additional cost to the restaurant would be wiping my table after I leave, and potentially bussing it if I don't (which I always do, but some people don't).