Oh no! You have been exposed to radiation, and a mutated hand has grown out of your stomach! What is the best course of treatment?
Sure, you could take a hit of purifier serum, but you might lose one of your useful mutations, or might not have any. So why take the risk of losing your superhuman abilities just to get rid of that wretched mutated tail or horns, when the most obvious option is available: cut it off. Either use a bone saw and anesthetic, or go jump in an autodoc and program it to amputate your extraneous limb or other mutated feature.
This would obviously not work to remove most mutations, but would be useful to remove some of the more noticeable ones, like tails, horns, etc. If cybernetic prosthetics ever get implemented, amputation and replacement of significantly mutated appendages (ex: tentacle legs) would be possible.