I see that a lot at Buc-cee's stations down here. Many of them have 50 or more gas pumps and often most of them are occupied, however, I often see that quite a few have no one actively pumping gas. They are inside getting something. At most times, that doesn't affect anyone, but when it is busy, it sucks if you are looking for an open pump.
I have also seen people do this when someone is sitting there in line waiting to get to the pump.