https://join-lemmy.org/docs/users/03-votes-and-ranking.html
"New Comments: Bumps posts to the top when they are created or receive a new reply, analogous to the sorting of traditional forums"
I feel like this is underutilized and can be really good for keeping old discussions alive and reused. It brings us back to the old school forums ways. On Reddit you see the same questions being asked over and over again every month or so (especially like on r/movies), if they had the New Comments sorting method then they wouldn't have to do that. And if you could subscribe to a post to get notifications about new comments that would be even better.
Now I'm also thinking Lemmy could have a Mixed sorting option to combine some of the main sorting methods, so you could see posts from Active, Hot, Top 6 hours, and New Comments all mixed together.