It’s used in the context of a micro-blogging platform where your feed consists of individual posts that don’t show the whole comment thread. If I replied to a post on mastodon, my followers only see my post on their timeline unless they click on my post to see it’s context. A quote post can be used to present someone else’s post to your followers, with whatever you want to say about it.

The bubble would be the actual post itself, you know? Like having the full post within another post. Similar to what you just showed but clicking the bubble brings to to the original post.

It’s like a repost, but it lets you add your own post to it and shows the original post as a quote bubble.

The biggest advantage of federated social media is that there’s multiple servers. I know it can be a rough point for new users, but most people can just join whatever the largest server is and they’ll be perfectly fine. You need to pick a server because lemmy isn’t one website, and it shouldn’t be one website. People should be able to host an instance if they disagree with another one’s moderation/rules, and spreading the load across many servers helps to prevent large scale downtime when servers go down. All of these advantages can coexist with new users just being pointed to lemmy.world.