If a tank is relatively empty, it's possible for air to be sucked into the fuel pump, at which point it could air lock or cause cavitation damage. This is in ad

If a tank is relatively empty, it's possible for air to be sucked into the fuel pump, at which point it could air lock or cause cavitation damage. This is in addition to there being less fuel in the lines which require it to run at a higher rpm to feed the engine. The higher speeds and uneven flow will lead to higher bearing loads on the pump shaft. Another commenter already pointed out the heat issue since the fluid acts as coolant.