CO2 adds flavor, think water vs seltzer. It also dissolves well in water, beer, wine etc.
Nitrogen. I had a 4 head wine tap in a bar I owned and we used a nitrogen (pure Nitrogen at over 2200psi. in the main cylinder, not beer gas) system to pressurize the 5 gallon kegs. The wine came out with no fizz or change in flavor. It was the same from the tap as it was from the bottle.