ultimately it can give you an endorphin boost because it is a bit of a shock to the nervous system. I spent quite a bit of time doing it and still frequently take a cold shower for that reason. I think it can be a good reset when life is stressful. Kind of like breathing exercises, it takes you out of your head and puts your body in physical survival mode briefly.

That said I have deep dived on the research and it is very spotty and inconsistent. Heart benefits, circulation, and brown fat are questionable. Brown fat especially is very unlikely unless you are going to extreme lengths. From my understanding brown fats come when you experienced prolonged cold. Like and mountain man living in extreme weather for the whole winter. To get the equivalent you would need to cold plunge for a month at 20-30 sittings maybe even twice a day. Pretty hard to sustain that.