Seems rather pointless to me, why would I want to see what someone's commenting without context? Yet, if I want context, wouldn't I be looking at that post anyway?
I kind of like it already. Sometimes I just want to read articles, but sometimes I'm interested in reading user discussion. This kind of easily lets me know where people are "chatting".
I think you'll find yourself using it. We had something similar on our end, and we kept finding ourselves using it. As the people you follow often comment on posts without sharing, it can lead to finding good discussions you might otherwise have missed. Give it some time, and see how it plays out for you.
It might be useful if you get bored and want to know what people are talking about. You may have followed someone because you liked how they contributed to discussion. In that case, looking for what they've commented on is as relevant as what they share/post. Or, maybe you're bored and used up your feed, or are bored of your feed. Looking at comments would stimulate you differently, if you were interested. If you see a comment you'd like to know the context to, there's a link to the post right there. Some people could consider chatter to be a superior feed: in your normal feed, those were posts users were interested in enough to share; in chatter they were interested enough to say something about it.