As Koltron said: it gives a soft yet punchy toplight which is more flattering than direct toplight. The main advantage of this technique is that you actually light the entire room without having to place lamps all over the place, trying to hide them. It makes finding the right camera angles for composition a lot easier/faster since you don't have to worry about lamps/flags/stands all over the place. Once the rig is up in the air (which takes about 10 minutes; if the rig itself is built well) you have total freedom.
One thing with this technique: make sure you measure, measure and measure some more! You have to know how bright the background walls are going to be, you have to know how bright you want the people in the room to be, on the various places they are going to be! I didn't give this thought but in the end it turned out okay (lucky for me!!)
The reason why I liked this over bouncing fresnels from the ceiling is that you can have a much larger area of illumination without it becoming too soft. If you would bounce a couple fresnels to the ceiling you would have an entire, big circle. In this case you have a lot of very small 'circles' spread over a large area. It does give a slightly sharper look on the skin than a normal bounce from the ceiling I think because there's direct light hitting the face from all over the place without causing too much multiple shadow effects.
Another advantage is the energy efficiency (direct light vs. bounced light). In this case I didn't have a lot of power because the building was very old and had old school wiring in the building. Couldn't afford a fuse blowing on me while shooting. I think the director might have killed me on the spot :p
Although it gives a flattering/natural top light look, the actors' eyes don't usually pick up a good amount of light (I didn't realize this on set). So it might be useful to add an additional reflector to solve that little problem.
Also: make sure the rig is far away from the walls especially if they are white; otherwise you might have to use a skirt. Usually one thing to mess up the mood of a room is having too much light: as you can see in these ultra wide shots. The wall behind the band turned out too be a bit too bright; could have been a stop or 2 less.. ah well, better next time
here's some comparison:
2x 1K PAR bounced off ceiling @ f 2.0 / 800iso (to light one small classroom)
hex rig about 1.5K @ f 4 (or thereabouts) / 800iso (to light a big room)