Not sure if you mean threads or posts within a thread. Threads go in order of the original date posted. Many of us use the feature to show active in last _____ (24 hours, 2 days, 7 days etc). That way we can go directly to the threads that have recent activity. You'll also notice that threads with new posts now have the topic sort of highlighted. I havent played around with everything on the new upgrade yet tho.