Do I need to cancel my ED visa before leaving Thailand, or will it be done automatically?

Dear admins and group members. I would like to kindly ask a question. I saw a post recently about this but now i cannot find it.

I am on an ED visas last extension of stay, which will expire on the 29th of September. On the very same day, I'll fly out from Thailand.

I read recently I should cancel the ED visa before i leave. Can someone explain to me please, why I have to do that? The school doesnt reporting that automaticly I'm not a student anymore? It will not be cancelled automaticly when I am leaving the country? I am not planning to come back for a quite longer period, tourist visas, ED visas, or any other visas not in plan for the near future. My only purpose to come here again would be to visit my girlfriend and her family for one or two weeks, periodically. Can I have any problem if I not cancel my current ED visa before i leave?

Apart from that, what do you think, what are the chances to come back for short periods periodically, after waiting a couple of months or even a year? Somebody have experience coming back to Thailand periodically for short periods? I understand theres no guarantee and should prepare the cash and onward ticket to make sure. I am just wondering what are the chances. Also ready for being questioned by IO, have many proofs such as photos and family members.

I have history staying in Thailand, one VOA with extension, and one ED visa. In total 1 year.

Thank you so much.