Why would one choose to use Nitro vs CO2 as a beer gas? Some beers have taste different on Nitro vs CO2. I'm sure there is science behind this. Why choose one over the other?
In general, nitrogenation imparts a creamier, smoother texture to a beer. The bubbles are smaller in size than CO2 bubbles, and the reduced solubility results in a thicker beverage, which is both delicious, and results in that visually appealing 'cascade' effect. 

Also, you can do this with a Nitro beer. And that's awesome.