Saver awards just require less miles, however there is a limited (sometimes very limited number of saver award seats open on a particular flight/route. If you are 1K/GS there are more saver award seats available but it can still be pretty limited, especially on popular nonstop/long haul routes. Otherwise there is no difference, except the number of miles you use to book the trip. If you have certain levels of status you can always book a saver award if there is even one seat left on the plane so it's good if you need something last minute and the cost is astronomical. More info here: http://united.com/web/en-US/content/...vel/types.aspx