Aside from some very niche cases (like the one above), dual monitors are useless for gaming. In my opinion, triple monitor setups are almost equally ridiculous (based on my experimentation with Eyefinity on 3x HP LP2475Ws). If you want more immersion, then get a bigger monitor. Contrary to what a lot of people seem to think, vertical size adds to immersion too. I don't see the appeal of viewing the game through a segmented bunker slit, nor the point in wasting a significant portion of your GPU horsepower on rendering distorted garbage in your peripheral vision. Eyefinity/Surround seems even more redundant now that there are plenty of ultra-wide monitors on the market.
For productivity sometime three monitors can make sense, but with the advent of large 4K monitors I probably wouldn't bother anymore.