When I was racing motorcycles, this idea was widely promoted as well, as a way to maintain consistent pressure and performance. To be quite honest I never noticed a difference, even while racing in all kinds of conditions for different lengths of time between 8-lap sprints and 8-hour endurance races. I guess when you're absolutely at the razor's edge and that very small difference might turn into a winning advantage, maybe it is worth the trouble. It really wasn't for me or any of my teammates.

Normal air is already 79% Nitrogen anyway, so you're just removing the 21% variable of Oxygen and other trace gases.