It's bad programming practice. A function has to return a value, but if you were able to gosub back out of the function without returning a value and go absolutely anywere in the code, you would/could be storing up huge problems for yourself.
I can't really think of any reason you'd ever need to. Logically you would just call another function instead.
I can't really think of any reason you'd ever need to. Logically you would just call another function instead.