Great question Christian. Here's the reason we have that option available to our users:
Exceptional tournament scores are accounted differently. Here's the relevant info from USGA rules:
Q. What is the effect of a tournament score on a player's USGA Handicap Index?
A. A player whose scoring record includes two or more tournament scores that are exceptionally (three or more strokes) lower than his or her USGA Handicap Index will be subject to a reduction in Handicap Index. If your club uses a computation service, the adjustment is probably done automatically. If not, the Handicap Committee must follow the procedure shown in the manual. After a Handicap Index has been reduced, the Committee can further reduce or override the reduction of a Handicap Index. A USGA Handicap Index reduction for exceptional tournament scores is calculated at each handicap revision and may vary from revision to revision based on factors outlined in Section 10-3.