I've heard that over-filling the fuel tank in modern cars can damage something. I'm not talking about forcing fuel into the fuel tank under pressure. Just topping it off past where the pump shuts off. I can't think of anything this would damage -- permanently I mean. Where you'd have to fix something if you did it.
I understand doing this isn't a good idea from a safety and environmental perspective. It could cause a fuel spill or could saturate the evap canister, which would allow gas fumes to leak out into the atmosphere. But I'd expect these issues would resolve themselves after a few miles, once the gas tank became less full.
Just curious, beyond the above, what could possibly be permanently damaged by over-filliing the fuel tank?