I was a little confused at first. As the announcement says, this is a complete replacement for the existing Drive app. No idea why they thought it was a good idea to rename it (and to use the same name for a separate application for Photos...).

I ran the install, and it appears that the main difference (other than UI) is that you can easily add other folders from your computer to your Drive now.

Looks like this allows you to select folders outside of the Google Drive folder to sync into the cloud without moving then into the Drive folder.

If it's backup, it should not work the same way: deletions should not be synced for example.

It doesn't take anything away from the current Google Drive client. It adds more features such as adding more folders to sync, choosing whether the images in those folders get synced to Google Photos, adding USB media support, and deletion options.

It also has a lot of bug fixes over the older client.

Or the google photos uploader? Backup and sync?