Handicap awards are the preserve of the rookie riders (No offence to Jamma). In the early days your times come down very quickly, several minutes at a time. Once you've reached a certain level improvements tend to be in seconds and the chance of bagging a handicap award are fairly slim.
I remember a near riot at the end of a 25 mile TT many years ago when three members of a club who only did road races entered the event when they had a free weekend. They were all first cats but with no TT history they got beginners handicaps and swept the board, taking all three places by something like twenty minutes over the next man. It did not go down well.