Driveshaft "balancer"

[GSR70Y]

I know it doesn't hurt to keep it on but Is this hunk of rubber really neccessary?
what does it suppose to do?

 

[Jazz9]

If it helps the vr4 frontcut and the 2 x gsrs that i have dont have them.

 

[mrcyborg]

i have been told its more to balance the weight between the shalfs and help with torque steer.

 

[GSR]

I heard it only reduces vibration :?