I just see so many disadvantages on running your own instance:
First and foremost, you need to rent a webserver and a domain.
Then, you need to setup SSH and TLS, and to configure your server as to lessen the chances of you getting hacked/DOSed, and setup some failsafes in case someone still manages to hack you.
Then you finally install the Mastodon/Pleroma/whatever and configure it to your liking.
And after all of that, many issues may still pop up at any time. What if your instance can't federate with others? And what if you get DDOSed? Lots of things can happen, and none of them seems fun.