It has one good use case, IMO: when you want to mention someone on Twitter at the start of a tweet but without solely directing the tweet at them like a reply.

It has one good use case, IMO: when you want to mention someone on Twitter at the start of a tweet but without solely directing the tweet at them like a reply. For example: "So @otherperson built this cool thing..." Some people use a single "." at the start of a tweet to the same end but I think it looks hacky.