1) Ability to have multiple contributors to a Picasa account/album (or whatever the name now that Picasa is in Limbo).
My wife and I both take a lot of family pics on our phones. Rather than having 2 separate public galleries, we use my account to display all the pics. Easy peasy for me. Not so much for my wife who e-mails me the pics, which I then upload.
2) Save from G+ to YouTube.
I also take some video. G+ auto backup is so convenient. I still have to post to YouTube separately. They should allow you to save the video from G+ to YouTube.
3) Same as in #1, have multiple contributors to a YouTube channel.
For all the same reasons as #1.