Usually people soak their snakes when the snake is having a bad shed, but other than that no need to soak them, unless you maybe wanna give em a little bath haha
IMO its not really a required thing to do. Generally if one of mine has a bad shed they'll get a soak by me, but otherwise I just make sure they have a water bowl with enough water to soak themselves in, and let them take care of themselves..they usually know when to soak themselves.
Oh ok I'm still learning. I have soaked mine to induce a pee - which it worked. I also was instructed to soak my Mojave when I had to give him antibiotic injections - something about keeping him hydrated while the meds were in his system to protect his kidney or liver - I can't remember which.
Bad sheds, when on meds, and also constipation. Bad sheds and constipation are signs of dehydration. I also soak during cooling to make sure they stay hydrated and to empty any residual bowel movements.