Anecdotaly, I find melatonin usage helps my brain rewire itself every night. My belief is that increases the number of connections and associations that various concepts have, and it also elevates my mood. Not bad for something that costs mere pennies!
During the time I had almost no sleep, I would take quite a bit of melatonin in a desperate attempt to get some kind of rest. At times I would pop 25mg or more. I found there were no side effects, except perhaps being sleepy for the next couple of days.
I've also quit a number of times for various reasons. Just a few months ago I quit for three months due to surgery. I found quitting to be completely symptom-free, which kind of amazed me. I figured with years of usage, quitting would make it impossible to sleep. I based this opinion on numerous studies that show when you replace a naturally-occurring hormone with a supplement, your body stops producing it. Instead, I slept fine. Once I was out of the no-supplements period after surgery, I started back up with the melatonin. No side effects, and I almost immediately noticed an increase in creativity and mood.
I'm a supplement junkie. It's that irrational thing that I do, my black swan interest. Yes, I know, most of the market is just BS and marketing hype. But not all of it. Melatonin is one of the 2 or 3 supplements I use that I believe really make a huge and immediately perceivable difference. Can't recommend it highly enough.