I find these reasons by Jesse Squires really compelling, enough to re-activate my Facebook and Instagram accounts sometime soon:
Regardless of whether or not I choose to continue using these platforms in the future, I prefer to retain the accounts for historical reasons and leave them vacant — at least for now… This preserves (at least the shell of) my online “identity” and prevents someone else from taking the usernames that I used for so many years. I would rather someone find my old, vacant accounts with a message to contact me by other means, instead of finding some Internet rando and wondering what happened — or worse, mistaking that other person for me.
On Instagram, after deleting everything years ago, I now keep a small handful of posts — 9 to be exact. When I post something new, I delete the oldest one. If ever decide to leave the account vacant, it will be quick and easy to do. This is how I use these accounts in ways that keep me in control.
At the end of last year, I downloaded all my data from Facebook and Instagram, so deleting all my content and keeping my accounts open there (though unused) seems like a good middle ground. I deleted Twitter years and years ago, so someone else has already taken up my old username there (which is okay, but still kinda sad—a feeling I can’t quite wrap my heard around yet).
On a side note, over the past week I’ve been getting emails from Facebook with a security code to login. I think someone out there is trying to get into my Facebook account and possibly claim my username as their own. I think this act alone is shaping my thinking on this.