I'm not sure if Mastodon users see long replies from Friendica correctly, but...
I spun-up a mastodon server for potential business purposes after making a couple of accounts on other mastodon servers because somebody told me it was normal to make an account on each server you want to be on. Their reason for that was you don't get to see the local community feed of an instance if you aren't on it. I didn't know it at the time, but that is a bit against the grain of the Fediverse, despite it being true in practice.
I wasn't that into having multiple accounts. I let a few of them go fallow, and at least one server isn't on anymore.
My instance hit a wall during an upgrade and stopped working. They made it more for Nginx systems than Apache systems, and I have a lot going on Apache. I looked all over the Fediverse for what to do instead of Mastodon and settled on Friendica.
The reason I took you on this diversion is the main reason to have multiple identities on the Fediverse should be based on how you want to express yourself. Friendica has a Facebook level of posting, where you are writing microblogs to interactive long blogs including embedded content. Pixelfed is the new cool kid and is a replacement for Instagram, Snapchat, Pinterest, and other photo-heavy social media options. There are so many nuanced choices, but Mastodon, Friendica, and Pixelfed get you pretty far.
Since you can follow anybody on any Federated system and get their updates, the reading aspect of content is independent of the platform. How you produce content is very platform dependent. That's where multiple accounts matter, but you won't have the same followers on the various accounts, so that makes your outgoing content distribution iffy.
Like you said though, business and personal life seem to be a natural separation. Wherever a person does "code-switching" is a place they would want a different identity. I spin two Friendica instances now; this is the business, and the other is personal.