Ballast left in simply adds supply inductance, and this is actually advantageous in increasing tube power supply life, as it will clamp the high voltage spikes present on the supply and limit the energy put into the power supply by them. Will dissipate some power, but likely only under 2W from the DC resistance of the wire, and as the LED tube runs at a very much lower current the voltage drop across the ballast left in will be minimal.
I have done that, plus have had a few with the ballast removed (electronic ballast removed, magnetic ones left in) and the ones with the magnetic ballast left in are still running 4 years later, being on 24/7/365. The ones without had around half the LED tubes fail in under a year.
One advantage to leaving the magnetic ballast in is that, if somebody replaces the LED tube with a regular fluorescent lamp, the end of the tube will not shatter on power application, as the filament is violently blown open circuit and arcs inside the tube. As they likely will not have turned off the power, not having to suddenly deal with a lot of shattered glass and blast right above your head is a good thing.