Three features are the source of an increasing amount of anxiety when it comes to instant messaging: read receipts, online status, and what I call "typing now... don't hold your breath" mode
What Read Receipts do accomplish is to tell the recipient that the sender now knows you have seen their message. Thus, the clock begins to tick to when you, per some unwritten social norm — which differs by sender and group — should reply or else you are ignoring that person.
About the feature "online status":
But now, everyone is essentially online all the time. There is nothing unique about it and you may don't want to reveal others that you are awake at 2am.
About the "is writing back" feature:
This is partially why I call it the "don't hold your breath" feature. You could be waiting, staring at your phone, ignoring the many other things you could do in that 30 seconds, and for your troubles get exactly... nothing.
How does this add real value to anyone?
These 3 annoying points are already solved by emails as it does not exist at all.