Well you shouldn't run it down all the way anyways. It is bad for your fuel system, namely your fuel pump. When you run down generally below a 1/4 tank especially when cornering or making turns the fuel left in the tank will slide around more and may cause you to momentarily interupt fuel flow which in the long run could wear out the fuel pump early.
Well not only that but it also sucks up all the crap that has settled at the bottom of the tank when it runs real low.