Actually, I just realised this morning. New is even more useless, it only shows New threads. This morning for example, it's empty despite new posts in 3 threads.
Unread is also useless because it only shows topics I have to opt-in to track. It is essentially the Subscription folder on the old forum.
Latest shows latest topics in a list, it's good for me as I usually do a Today's post search and browse by threads. BUT there's no way to distinguish between new posts since my last visit and thread titles I've read last time. grrrrr