The Sympathetic Nerve Carries Many More Signals
Than Just For Sweating

Another thing doctors don't tell you is that the sympathetic nerve also carries thousands of other vitally important messages and nerve impulses throughout your body all at the same time, much like a fiber optic cable. And these messages carry crucial information which control vital organs such as your heart, lungs, eyes, body temperature, stress levels, circulation, sexual function, bladder control, salivation and a whole bunch of other really important stuff that keep your body functioning correctly.

And when your sympathetic nerve is severed in order to stop this one signal (for sweating), all of those other pathways  are irreversibly damaged as well.