For people who also have the lemmy.world home instance and who are using the Lemmy Web UI as their client, it doesn't matter.

But for others, one generally wants to link to communities using this syntax:

!community@instance

So !insanepeoplefacebook@lemmy.world

Rather than:

https://lemmy.world/c/insanepeoplefacebook

If you use the "!" syntax, each Threadiverse instance automatically generates hyperlinks to view the community via themselves.

Otherwise, users on other Lemmy home instances using the Lemmy Web UI will leave their home instance and view it via lemmy.world, which won't let them comment and upvote and subscribe and such.

Users of other clients who have lemmy.world as their home instance may be thrown into viewing it via the Lemmy Web UI rather than their favored client.

Piefed tries to detect and rewrite https links to Threadiverse instances like this and make them point at the local Piefed instance's view of the community, so an https link may also work for Piefed users, but that approach brings its own set of complications.

Generally, it's just best to use the !community@instance syntax if possible, since it avoids a bunch of problems for other users.

Just one of the wrinkles of having a system that's federated across multiple instances.