I was examining a cat one day and there was just something funny looking about it. I couldn't figure it out. I finally noticed that his whiskers had been "trimmed" to be even with his cheeks. The lady was foreign and thought it looked "cute". I hope I dissuaded her...I was so shocked that anyone would even consider this, I may not have been my most diplomatic!
Several good reasons have been brought up, but one more is that the sensory cells at the base of each whisker are highly specialized and exquisitely sensitive. With the whiskers blunted instead of tapering to that fine, delicate point, each time he bumped up against something, it must have been a very strange and unpleasant sensation, like having a stick jammed into your cheek!
BTW, identical cells are found around the base of each claw -- another reason NOT to declaw!!
Cheers,
Dr. Jean