EFF is Leaving X

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 the instance’s admin team.

fedi.tips

Using allowlists on Mastodon servers through Limited Federation Mode |...

An unofficial guide to using Mastodon and the Fediverse