[Scuderia_Turini]

The belt drive to the other axle is just extra friction to consume motor power. Where there is a long motor shaft to one axle, that will sap motor power unless the shaft is perfectly true and has a locating bearing at the end beside the pinion.
So, as Chris says, unless the track surface is raid-type or has some form of coating then removing the secondary drive kit will mean that all available motor power and torque goes to the primary drive.
However, some events require the all-wheel-drive to be retained.

Leo