For couple of reasons.
It gives the audience a clear view, uninterrupted by softboxes or umbrellas.
It also avoids having to reset the lights every time you take to the stage as another shooter is bound to have changed just about everything,with ring flash you have just one light to consider, it gives cool high fashion look too.
It can look a bit 'samey' though.
While we were setting up the show we had shot some 'straight' test shots which were fine (always get the safety shot in the bag first!)
Safety shot mission accomplished
I thought it would be interesting to try using the Profoto ring flash off camera.
On the floor
Yes, that's right on the floor, at 45 degrees to the model
I did it as a bit of fun, but I was knocked out by just how funky it looked
Still preserving a harsh but wrapped round look, with THAT shadow
I will be using this trick again, at shows and on 'real' shoots
Breaking the rules is fun!