When we were first married and he would on occasion say, “How long has your low fuel light been on?” To be honest, I just thought Jeff didn't want his beloved bride to run out of gas and have to sit on the side of the road. The truth was that he didn't want to have to replace the fuel pump in my car. That, and he didn't want me sitting on the side of the road either.
When you run your fuel low consistently, it can damage the fuel pump. If you have dirt in the bottom of your fuel tank, it can block the fuel filter. It’s a lot cheaper to keep your fuel at least at ¼ tank than to replace these items.
Also, don't trust the range of miles left until you run out of gas as indicated by your car. We’ve on occasion had vehicles towed in that had ‘just quit running’. After determining that they were simply out of gas, and talking to the driver, we would sometimes hear that they thought they still had ‘70 miles left’ before they ran out of gas. Those indicators aren't always accurate.
Thirty-one years later and Jeff hasn't had to replace a fuel pump yet on any of my cars. Just don't ask me about my brake pads!