You don't need multiple accounts on Mastodon and the Fediverse, but in some situations they can be very useful. For example, you might want to have separate work and personal accounts, or specialist accounts, or accounts on different types of Fediverse server with different features.
All the apps support being logged into multiple accounts at once, as do the websites and web apps.
@FediTips you mentioned you don't need multiple accounts on the fediverse. Fediverse includes also group support. While I love mastodon it's mainly focused as a Twitter alternative. But not aimed as a reddit alternative. https://github.com/mastodon/mastodon/issues/139
Which is fine. But keep in mind if you want to use software that does require specific implementation of activitypub you might need other software, which might need another fediverse account.
@FediTips I think the main sofware which is used now is lemmy and not guppe. Also I'm the creator of the fork mbin, which is a fork of kbin, mbin is focused on the community.
You just might want to extend that page with more possible options. And mastodon isn't really great in handling groups too bad.
Unfortunately I can't list Lemmy (more info: https://mstdn.social/@feditips/106835057054633379) but I have an article about Kbin linked to at the bottom of the page. I'd be happy to add Mbin to it if you have more info on it?
@FediTips I disagree : official Mastodon web client, native on every server, doesn't support being logged into multiple accounts. We have to log out to log in our other accounts. Elk offers the possibility.
You can be logged into several accounts at once on the web client, as long as the accounts are on separate servers. They can be kept open in different tabs, or saved as separate web apps.
If your accounts are all on one server it's trickier, but that's not recommended anyway because if the server goes down all your accounts go down too.