it really comes down to personal use. usually the more uneven or rocks in
the area you will using you will want to set the skid up high to avoid the
scraper bar from catching and help from rocks or other small objects from
going through the unit and damaging it.
From new when I set it up I use two 1/8" piece of flat iron under the
scraper bar (with the unit not running) to set the skid height, after that
it is up to the customer to choose his final setting.