This comes really handy when we have a particular set of photos which we don’t want to appear in the main timeline. The photos can be archived from the overflow menu and will be listed in a separate space of its own. So all your embarrassing photos which you want to keep but don’t want to be exposed when launching the app in public. This too is a tidy way to manage your frequently viewed photos in case there are any.
The feature is rolling to everyone right now without the need to update the app from the latest build. In case you haven’t got it make sure you are on v2.15 of the Google Photos app.