It is not a good idea to let the fuel level get too low. Most cars these days the fuel pump is located in the gas tank. This location is best to keep the fuel pump cool. The fuel actually cools the pump while in use. So you can only imagine what happens when the pump runs dry. Heat will burn it up. I've done this before in another car (older american car) and had to replace the pump. No fun. I learned my lesson and fill up at 3/4 tank.

I don't know this for a fact, but there should be a fail safe circuit to shut off the car when the fuel level gets too low. But why take the chance?