I try to use hashtags for topics specific to my comment and not already covered by the thread, the comment(s) I'm replying to or the magazine in general since people know they can look under that thread to find more of that topic anyways. Now admittedly, I may not be that consistent with this and might make some tags that fall a bit outside the topic but that's at least my goal. I wasn't using Twitter that much before my Reddit migration and I first started using hashtags with Kbin so I'm not sure how exactly they should be used.