I do not use Mastodon, but it is my understanding server admins can (and do) restrict federation with other instances based on either block-lists or allow-lists. If your server admin has blocked an instance you would like to access then (I think) yes you might have a need for multiple accounts.

I think in general this is just used to protect users against harmful content though, as defined by…

People come to the Fediverse to connect with others around communities and topics of interest. We’ve seen people enjoy their time on Mastodon the most, when they can follow and engage with individuals and organisations that have interesting things to share. We want to help those who are new to the Fediverse discover these communities more easily.

Back in October 2025, we shared our initial ideas…