That is the main thing, yes, but it would also allow for better coordination among the instances for migration efforts. “Fediversed” Instances can keep of redditors that migrated, can have more attributes to display for people when selecting a instance, can accept or reject a Redditor based on certain criteria (e.g, account is too new, or was flagged as a spammer, or is posting a language different from the main language in the server, etc)