Sliding backband

Can anyone tell me what the advantage of a sliding back band is? When I hook my cart up and put the shaft through the first loop the back band always slides down a few inches from the weight of the cart. Of course, when I insert the shaft on the opposite side it equalizes. I can see that with a stationary back band the shaft might initially pull the whole saddle off center. Is that the advantage?

I think it is made to slide to help the horse when he,s moving I,ve never really thought about it to be honest,but I suppose it has to shift a small bit for uneven ground and such,

A sliding back band is for fixed shaft vehicles so that if you go over rough terrain it slides and doesn't put stress on the horses back. If you have independant shafts you need a fixed backband because they do not have enough pressure to equal them self.

exactly what I was trying to say but coulde,nt quite explain it

Thanks guys.