The downside to individual servers, and micro-communities, is the cost and maintenance of lemmy instance. Its more scalable, reliable and cheaper to have a bunch of relatively low-churn communities exist on one bigger instance.
The upside is that the rust community gets to own its own data. If programming.dev decides to shut down tomorrow, and posts and comments made there are gone. Lemmy doesn't mirror or cache... all that data lives solely on the server ran by somebody.
I'd vote lemmyrs at least for now until a governance and stability model is figured out to ensure these conversations don't go into /dev/null like /r/rust (sort of) did.
If say the Linux Foundation or a similarly large open source foundation (Apache, FSF, OSI, etc) decided to host a larger "open source" server, I'd consider moving there to improve discoverability and lessen the burden on the rust community itself
Yes. If you run the server, then you are the source of truth of that community. All other servers that federate your community query your server to access the community and show it to their users.
So if you run a server and a community explodes there, you might only have 500 users on your instance, but you might have 50k users reading that community and interacting with it from other Lemmy instances, thus your server needs to scale to 50k users worth.
And ever more essential, your server is the source of truth of that community. So if your server is hacked or corrupted or deleted, that community is gone. Other instances don't mirror it (except for temporary caching), so the Lemmy network essentially is a trust network of other people maintaining servers long term (and each inventing a monetary system to pay for it). I still think the network might be better than a centralized system like reddit, but it definitely has a lot of growing and policies that need to be sorted out very soon