In addition to a large instance being less likely to shut down and (presumably) having more resources, there's an additional advantage to being on a larger instance: you have a more comprehensive "All" feed. Since federation with a remote feed isn't established until (IIRC) someone subscribes to it, an instance with a larger user base should contain more subscriptions to a wider variety of content. Of course, not everyone will like that and you lose out on Beehaw content if you're on the two largest Lemmy instances, but I think it applies in general.