1. make the weight of the whole car more concentrated in the chassis (commonly known as the lower disk stabilization)
2. most of the time in the climbing car climbing up, when the car lying on the slope to increase the wheel position downforce, more downforce can provide more friction between the tire skin and the ground (commonly known as the grip), coupled with the car's front-heavy design (such as the motor, the battery front), the overall increase in the front wheel grip, reducing the possibility of the car's head back to roll!
Simply put, it increases friction and reduces the head-up rate, but it is not recommended to add it to the wheel hub, which will make the drive shaft in the axle more stressed and easily lead to damage. It's better to put it on the side of the axle, the axle housing, or the C-seat than on the hub.
Of course, some axles don't have an on-axle weighting option, so you'll have to go to the hub.