Interestign that Stephen Frink prefers one strobe for wide angle.
When the Nikonos and Nikonos RS were the predominant photo gear being used lots of photographers shot their CFWA with one handheld strobe. In many (maybe even most) cases it makes for a more interesting image. Unfortunately in the digital age holding a housing with one hand is difficult for some photographers and the method has been almost forgotten. Plus strobes specific to digital capture aren't as powerful as some of the blow-torches used in film's day, so two are sometimes mandatory.
"painting with light" seems like such a predictable thing to say about photography, but that's what one could (and can) do with a single hand held strobe
On the other hand it takes an accomplished diver to dive with both hands full and not bounce around the underwater environment, and most of today's uw-photographers are accustomed to dropping a free hand to steady themselves, or worse.
In my humble opinion some of the more lasting underwater images over the years have been shot that way. Of course having the 15 and 13 to use didn't hurt either 