Every program you write that you intend to keep around for more than a couple of hours ought to have documentation in it.
Don’t talk yourself into putting off the documentation.
A program that is perfectly clear today is clear only because you just wrote it.
Put it away for a few months, and it will most like take you a while to figure out what it does and how it does it.
If it takes you a while to figure it out, how long would it take someone else to figure it out?