it is about "consistency" and presenting "content types" or "Recent Activity Types".
The Tab "All Activity" is still showing everything, same as currently.
It's not a big change, just adding a few more Tabs, so you can filter the "Recent Activity".
Makes it more interesting for the user to click on the Tabs to see e.g. at the Tab "Profile Updates" who has changed his Avatar-image or who has added a "Homepage-URL" to his profile, etc.
In our community people would love this, it was requested several times, the sidebar addons works, but, it's limited, we can only read the recent status. Now starting my own community but in the one I managed everything added in this social side converted itself in a more active site.