It is unnecessary (like plastic surgery), unless your the type that enjoys surgery just for the heck of it.
It is done with no anesthesia (when done at birth) and the child is left writhing in pain.
Aside from some cherry-picked statistics that anyone can conjure up, nobody has ever given me a good reason why is is a necessity (and if you're gonna go carving on my kid it had better be a damn important reason).
Well according to my husband...my son felt nothing when being clipped.
It has been the norm to use a local anesthetic for newborns since I was in my residency, 23 years ago. As a medical student, I saw it done regularly without anesthesia, but that is not the usual practice anymore.