Electric fuel pump wiring

I have always wired my electric fuel pump and ignition on the same switch . Flip on ignition switch to on and fuel pump comes on. Turn ignition off fuel pump goes off. Seems to me these to go hand and hand. 1) for safety. 2) there is no need to have one without the other. So my question is why do people and professional builders wire the fuel pump on a different switch from the ignition . I would say most of the race cars I see down here in texas are all mostly like this. Maybe there is a good reason to do it that way. I just don't know what it would be. Someone please tell me why ??