it really depends on how you work the horse, I ride at a dressage barn and the stable owner says that if you work one side of the horses back mroe then the other (to straighten the horse out) then that side should be moe sweaty. Haha my horse is very weird, we have had the saddle looked at many many many times and each time the saddle fitter says: the saddle is fine, btu on one side of my horse she sweats more! Haha even on her neck she does that... I think it might be because I probably get stiff on that side or something, lol, one mroe thing to work on!
But ya, what everybody else said(with somhting added form me): the saddle marks should be the same on both sides, unless you are straightening a drastically crooked horse
If there are no horses in heaven... im not going.