Adjustment means when the bolts on the stem are untightened, you need mechanism to compress head set bearings. If bearings is compressed (adjusted headset) with default star nut , then stem has to be tightened. After that star nut does not have  mechanical function , but it is like cover of top head tube only. If you install TrackHead , you need to remove default star-nut. Star nut extender is longer bolt and it provides compressing mechanism for adjustment. This function also can provide headset compression plug component, or long bolt with top and bottom washers.