The effect of the stock slipper is a big kick of forward torque .. a bit like a 3 gear I suppose .. taking some of the weight out reduces that effect.
If you want to try it for yourself, take out the tranny with motor and all still attached, and fire it up while holding it in your hand .. it's quite surprising .. you can then take bits off and directly feel what effect it has .. thats what I did ... my final choice of a fully stripped down slipper was because that was the most neutral of all the options ..