The basic idea is that it is wasting time. But this is no longer a factor as the gear change is instantaneous with Automatic GearBox.

Electric cars do not have a gearbox and just have one rotor. This does place them in a disadvantage when starting though as there acceleration is affected. Formula E cars, have started using a 3 gearbox for their cars in order to have a faster start.

So it is possible that the Roadster does have a gearbox.