It supplies B vitamins which are necessary for energy production and not found in great quantity in the foods normally found at aid stations. So, it is not used in ultras in the way it was originally intended to be used, but so what - it supplies ample quantities of useful substances. One thing it would be good to add is magnesium, as that is needed in endurance running. For short distances, follow the directions on the label. For ultras, skip the pre-load described on the label and take only during the event.
Some runners find it useful afterward for recovery.
My experience is that if you take it during the run, it is not needed afterward. But, try it for yourself and see what works for you. Just remember that it is not candy. The effective dose in an ultra could vary with conditions. What seems reasonable based on my experience is one at the start, and one every four hours or so.