Dual subwoofers are a great option for the enthusiast who can accommodate two subwoofers in the listening area. The benefits of dual subwoofers include increased dynamic headroom and a smoother bass response at more listening locations in the room.
Dual subwoofers are also harder to localize than a single subwoofer, which might be an important consideration for the enthusiast using very small speakers which require a high speaker/subwoofer crossover frequency.
Finally, two smaller subwoofers can often fit better into a room than a single larger subwoofer in terms of available floor space and visual impact, while offering similar or better performance as the single larger subwoofer.