If you're taking it once in a while to reset your circadian rhythm then it wont cause any issues.

As it is a hormone I'd agree with you that it's not a great idea to flood your body with it everyday. Men have an especially dangerous side effect from overdosing melatonin, it increases another hormone in your body, prolactin. This is not a big problem in Females, but in Males excess prolactin can cause liver and kidney problems. Taking too much melatonin can also cause insomnia, the exact opposite of what you'd expect. And to top it all off most supplements have way to much melatonin in them. The recommended dose is less than 1mg, but I've found 10mg melatonin pills in stores where I live.

Friendly PSA: Do your research if you're going to put anything in your body, food, medicine, or otherwise.