I am another case of a former two-strobe owner finding out that over time I more and more often only used one, and now am back to a one-strobe system. But I would not necessarily recommend that to others. As Doug indicated, WA in particular can use both the extra power and the ability to throw a wider light cone needed to cover your field of view. It is also true that with two strobes you can use one to fill in the shadow thrown by the other. I have never found that to bother me, but you should know for yourself how critical you are about image perfection. I do however notice that above water I rarely see photographers use two strobes outside a studio.
From a learning perspective I think it can be useful to have two strobes, assuming you have them or can borrow, so you can experiment and learn from the results. This assumes that you are at least a competent diver and find conditions where you can focus on playing with your camera. A pool or shore diving with a patient buddy will work, trying to do this while keeping up with a dive master or fighting a current will be futile and it is better to keep things simple.