Even though chunky monkey and I rarely agree on anything, I think she’s spot on on the “wither-shaving” being somewhat of an urban myth, if you will.
(one component of ULs being that it’s always something that a friend-of-a-friend heard or did or said, another being that something that might have happened once is being touted as a common occurrence).
The withers are the dorsal spinous processes of roughly the 2nd to the 8th
thoracic vertebrae. Taking a bit off the top of the might sound simple enough, but, there are a number of soft tissue structures to take into account, including the continuation of the nuchal ligament and its transformation into the supraspinous ligament, the dorsoscapular ligaments, several muscular attachments, as well as the supraspinous bursa.
The risk of causing permanent scarring, potential for damage/infection, and resultant chronic pain issues are not entirely insignificant, and would, for the most part, make this likely not worth the risk, especially compared with more benign ways of minimizing height, as in clipping all the hair, pulling the shoes and trimming as short as possible, and the old grain sacks on the back, tired pony tricks.