You no longer have to go digging through your tweets to reply to one with an update. Twitter has added a feature that makes it easier to connect an in-progress tweet to an earlier post. When you're writing your latest missive, you'll just have to pull down to see earlier tweets and tap the "continue thread" or ellipsis button to find an older tweet to reply to.
This is ultimately a new way to do something that's been possible for a while. It could spare you from scrapping a tweet if you forgot to reply, mind you. And if you're the sort to frequently update your friends on developing events (or correct earlier slip-ups), a change like this could save you a considerable amount of time.