Remember that the button at the top of the sidebar expands the options to disable federation.

Your home feed can default to "All," which shows content from all communities across all federated instances (not just Kbin and Lemmy) or it can default to Subscribed, which shows content only from communities you're subscribed to. Lemmy has a third option called "Local" which shows content from all local communities. Turning off federation for yourself in Kbin is similar to the local option in Lemmy, but allows you to still switch between All and Subscribed (ie, all local or subscribed local). Lemmy doesn't currently offer a "local subscribed" view.

The hamburger menu next to your name allows you to toggle between Subscribed and All. In the dropdown menu when you hover over your name, under Settings, you can select your default view (Subscribed vs All).

My personal preference is to default to subscribed and see content from across the Fediverse that I choose to see. This way I'm not missing out on any communities or magazines on federated instances that interest me. I sometimes switch to All with the Commented sort to see what the current zeitgeist is (where are the biggest conversations happening). I don't see much need to de-federate my view entirely since I can block communities/magazines, or entire domains, which means even under All I'm not bothered by content that I find annoying, offensive, etc.

For what it's worth - on the microblogging (twitter-like) part of the fediverse, we've had pretty great results federating with lots of instances, but defederating from the ones that have problems with hate speech, spam, etc. It's led to a much more positive vibe than Twitter etc because people aren't so afraid of some random person misconstruing something they said and jumping down their throat about it, and there's no algorithm pushing rage "engagement" to the top.

One of the problems we do have in microblogging land, is the main mastodon developer has tried to direct new users to his own instance, making it by far the biggest mastodon instance, and then did a bad job controlling spam - so the other instances were left having to chose between cutting off a huge number of real users, or being inundated with spam. Having all the kbin and lemmy instances federate with each other, except where there are issues, can make the network overall more resilient against any one instance being mismanaged or invaded by spammers and trolls. The users on that instance will have to move, but there will be plenty of similar-sized instances ready to welcome them, and if the magazines are also spread out, they can keep posting to the same ones.

(I admit I also have a selfish interest here - I'm posting this from fedia,io, a different kbin instance. I joined through a different instance than the main one to help nudge things toward decentralization.)

At least from my quick test right now, it limits your home page to posts within kbin.social. Not sure if it works the other way around, too, preventing your posts from going out into the fediverse.

Why would you want to exclude external users as well? The reason why you still saw that post is that /m/StarTrek is a local community

he is the mod on lemmy for a few anime and other things too lol

I had to play around with it a bit to figure out how this is working. Basically, if you post to a Magazine's "microblog" it uses the Magazine name as a hashtag. See: https://kbin.social/m/kbinMeta/p/433361. Paste that link in your Mastodon client and you'll see the #kbinMeta hashtag. So, if you want to follow the Kbin Tech magazine you'd have to follow the #tech hashtag in Mastodon. If you look at that Magazine you'll see posts there from Mastodon servers. Those are posts with the #tech hashtag. Posts that don't have a hashtag end up in the Random magazine.

If you dive into the technology behind it all you start to see that all of these different platforms are designed to show the same content in different ways. They're all based on the ActivityStreams protocol: https://www.w3.org/TR/activitystreams-core/.

Take the image object. If you post an image to Mastodon you see the text that was posted with that picture then the picture. If you look at the same picture in Pixelfed (similar to Instagram), you'll see the image first and displayed prominently, since it's the focus, followed by the text. In Lemmy or Kbin you'll see a small thumbnail that you can then expand to see the full image. Same image object type, different ways of displaying it.

I guess the point is, depending on what your interests are (microblogging, sharing links, sharing photos, etc) you pick the platform that most suites your need. Or, have multiple accounts for posting different content.

1. no, each server (kbin.social, fedia.io, lemmy.world, etc.) can have their own communities, since there is no centralized server that manages community names it would be impossible to track which servers already have a community with the same name
2. yes, that's the beauty of the fediverse! this post explains how you can do that. you can also view and interact with posts from other federated social media sites such as Mastodon if you are interested in that sort of thing