The reason it turns up in my comments is because kbin autopopulates our comments with tags, and I don't always remember to check where I am and delete that before I post.
On Kbin itself they're handy. Kbin integrates with Mastodon and those guys kind of need @tags to follow our conversation threads when they come to discuss our posts.
And on lemmys, the @ is useful for me to keep track of who I'm saying what to anyway at times because our threading can't handle some of the really big lemmy comment sections.