They've already been doing this in chat, I suppose this is a logical extension. That said, is it really necessary to see this or is it a step beyond what is necessary?
They're probably running out of things to implement that people want, so are now trying to shoehorn things in that people probably don't want. Probably as a result of new-found shareholder pressure.
The biggest barrier to using Facebook as a communication tool is not knowing how often other people check their messages or groups. This feature solves that and will increase the usage of messages and groups.