Thanks for all the replies. Some interesting stuff in there.
2miles600feet - to address your comment what I meant was something like this........we regularly follow the willo3c on arrival. However if it's not busy we sometimes get cleared from before AVANT to MAY with no speed control to land on 26L. This can cut the arrival time back by about 3-5 mins. If you have to rigidly follow a PRNAV arrival even if it's not busy there is no opportunity to make up any time.