What are the advantages of large ring strobes?

[nuffi]

I see them used quite a bit in pro portraiture, and I am wondering what there is to it.....

[Wilt]

Large, flat lighting, where the lens pokes thru the center.

Not unlike macro ring flash, where it is small, flat lighting, where the lens pokes thru the center.

Fashion mag photographers created the 'look' and it is now quite faddish. It is not good lighting that flatters the average subject (who needs all the help the face can get from 'short' lighting and the modelling of the face that is accomplished with fill vs. main ratio).

It's benefit is 'different', that's all!

[GarryEdwards]

As above.
Basically it's about relative size. Macro ring flashes produce the 'ringflash effect' at very close distances, pro ringflashes (http://www.lencarta.com/safari-portable-flash/fla006-safari-ring-flash-kit/index.php)can produce the same effect at greater distances, which obviously macro flashes can't.
Also, pro ringflashes have enough power at greater distances. Ringflashes produce very unflattering lighting but are excellent as fill light, as they're in the only place that can produce true fill light.