The dif can be used as a tuning option, but it is not recomened. Its sole purpose is to allow the outside wheel to turn faster than the inside wheel during cornering.

You diff should not have any slip in it at all. I usually run my diff on the tight side. Tighten the adjustment screw till the diff spring is compressed then losen 1/8-1/4 of a turn. An excessively lose diff will do nothing for performance and just wear out parts sooner. Don't confuse a smooth diff and a loose diff. If built propery, your diff action can be very smooth with the proper "tightness"

If you are running an a low traction surface, it is better to losen the slipper. That is what it is there for.

Good luck.

John