I think KOK is the most absolute and correct way to describe that part of a Fish. Here are just a couple reasons why...
1. It is mostly composed of fat and blood vessels...
2. When you are chilling around the tank (or park) it always gets in the way...
3. Weekley water changes that result in different parameters (IE Temperature) make it smaller...
4. The bigger it is, the more of a chance it will hinder eyesight...
5. Females don't have them, or if they do....(eww).......they are always smaller...
6. The bigger the better...
7. Above average size may cause back problems...
8. It is the prefered place to be touched/rubbed...
9. Having PEARLS all over them makes them way more valuable and appealing...
And Finally...
10. New-Borns are judged on potential size, and every father (or breeder) hopes their offspring are well equipt for the future.
Just my take on the subject.
Hahaha