The only time it would be an issue is if your evap system decides to check the integrity of the system at the same time you are refueling. It pulls the fuel tank down to vacuum and watches to see if the system bleeds back to atmospheric pressure. If you have the gas cap off, it cant pull vacuum and would set a large leak evap code. You could just clear the code with a code reader and move about your day. But the likelihood that it does this at the same time you are refueling would be extremely low in the first place.