To add on to what "Many Tentacles" has said, since shorter routing can mean multiple liaisons, you also have to introduce the human element. Some ATCO's are simply happier to give and accept shortcuts than others. I always like to know who I'm working with (based 400 miles away) sometimes I know I can shorcut the guys and just put it on the label, other times though, I could request two degrees left and be told, "negative, keep it standard".
First part of me goes
, but then again, he's completely within his rights to make that decision...