All yer gear is attached to "you" so you have a primary point of connection and a safety "cheater" strap. They are just wearing the harness vs a load bearing vest under the harness. Some of the older vests we used had the harness built in. I did this a few times at Ft Story VA and then during my career never needed it again......
Primarily a means of extraction. You think that looks barf-o-rama, you should try AIRBORNE!!