As a top down Twitter reader, I always load in a ton of new tweets and then quickly scroll to the top and read down. My logic is that if I don’t make it back through all of the tweets I caught the latest, and arguably most contextually important, news based on time.
Occasionally I have enough time to really read through my feed and realize too late that I’m scanning and reading tweets from my last session. A last read/scrolled-to marker in Twitter—synced with my mobile app—would be incredibly useful.