I perhaps I missed when this new feature was added, is this the first step in the view author only for a conversation?
I can see where having just the direct replies can be useful but does this include replying to someone who replied to the author?
A mouse over or a "?" might be helpful in rolling out new features so people can absorb the functionality as intended.
The conversation viewing options are almost as critical as the searching options and filtering in my opinion only of course.