As high school science tells us, atmospheric air is around 78% nitrogen, so there are no miracles in increasing that to 99.99% nitrogen. For example it won't reduce pressure drop over time, stop leaks or reduce punctures.

We use nitrogen in the race car tyres for consistency, as pointed out above there is variability in the air pumped straight from atmosphere, particularly humidity. The other, but related issue, for using nitrogen is the reduced pressure increase as a result of increases in tyre and wheel temperature. In some categories, during a race, we can expect upwards of 10 psi increase in pressure partially due to the separation (into hydrogen and oxygen) of any water vapour present. Using bottled pure nitrogen removes the possibility of any water vapour. In addition nitrogen expands at a slightly slower rate than atmospheric air. Hence we get 25% to 30% less tyre pressure growth during a race.


My view, there are good reasons for using nitrogen in race car tyres, not so much in road car tyres.


Cheers
Gary