system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it bad to let your car get below 1/4 tank of gas?

I've always been told it's bad to let your car get lower than a 1/4 of a tank or be on E with the gas warning light on. Is this them being paranoid or are there actual detriments to your car?
gpt
This is one of those things where there are no absolutes. 

There are obvious risks to running out of gas when driving with a tank that's nearly empty, namely running out of fuel or having insufficient fuel to make it to the nearest gas station. 

The bottom of the tank, especially in older cars may have sludge, dirt that fell in to the tank, flakes of rust, or water that may have condensed in the tank. Additionally in many modern cars, the tank is usually shaped to conform to some void in the vehicle's frame. Depending on where the fuel pick up is, and where the gas gauge is, it might not register the same levels.

So refill the tank when you feel the risk of running out of fuel justifies a stop at a gas station.