It's a simple shoulder strap with a shoulder padding area that splits revealing a passage way for the carry on handle to go through. See pic



The result is a briefcase that simply falls down all the way to bottom and front of your carry on bag which makes piggy backing and rolling your bag a breeze. Many times when your briefcase is really full it's sometimes a chore to bring it up to your stomach level (to chest level for shorter dudes) matching up the luggage pass through then putting the bag on top of your carry on, which puts more weight on your elbow and arms carrying the whole thing.

Of course there are the straps that come with your carry on luggage but I either lose it or won't bother with it cuz it takes some fumbling around right after you get off the plane. This strap is easy and don't involve any extra parts.
It sits like this below after just 2 seconds.

Just wanted to share.