I host my own instance for the same reason I self-host the dozens of other services. To have control over my digital services the best I can. I have a few server machines running various services. I run like 40 docker containers running at the moment. Lemmy is a set of those containers.
It cost me the electricity cost to run the server, plus the cost of my internet. I suppose you should include the initial hardware cost- my servers are basically my old gaming rigs. Not to mention the time investment to maintain another service. For me, it's worth it to self-host if I can.
Specifically for lemmy, I seen how overloaded the various major lemmy instances out there were, so self hosting could mean one less user on those instances. I also didn't see any significant drawbacks to self-hosting the instance since I can still join and communicate with all the other communities.
I tried out my own, one person instance, and I had a hard time getting comments to pull in. I would have to browse to the original instance to view all of the comments. Have you found a good way to overcome that?
I switched back to a more public instance just because I found the process of going out to view the content, back to my own instance if I wanted to comment, then back to the original again to keep reading the discussion very tedious.
Being on a more populated server seems to give most if not all of the comments directly.
When you first subscribe to a community it only pulls in the last 20 or so posts and I think a limited amount of comments, and then everything going forward. This seems to be a common point of confusion for a lot of instance admins.
Presumably this is to prevent a possible DDoS/performance failure vector as it would be trivial to setup a large swarm of instances on tiny VM's and then simultaneously start hitting massive communities from a single instance and requesting a large body of historical content.
Edit: Also when you first setup and start subscribing to a large number of instances, this initiates a LOT of communication and database writes. Lemmy still has some performance bottlenecks. Once everything is initially synced and settled it runs fine. I have a friend running their instance on a $5 Linode instance that only has 1vCPU and 1GB of RAM without any issues, and they're hosting users.
I ran mine for a couple weeks, and communities I'd been subscribed to from day 1 were still missing most comments on the posts unless I clicked through to their page. Maybe there was something funky with my install, but I used Lemmy's ansible scripts to deploy so I don't know what else I could do.