moving it backwards or forwards also allows you to use other belt sizes. there are at least 2 belt sizes I have found I can use on my Bravo. That's handy if your local shop doesn't have exactly the size you need.
also, I think Mike's theory on forward and backwards is exactly backwards. keeping the belt in a lower gear ratio longer by moving the engine forward should keep the bike in low gear longer. moving the engine back closes the front variator sooner, putting you in a higher gear, but allows your belt to variate up to the maximum point, thus faster.
you use cardboard in the variator to start the bike when the engine is moved back enough to allow the belt to slip. it works.