Pure nitrogen is heavier and denser than air. Scuba divers sometimes fill their drysuits with nitrogen; being denser than air it's a better insulator.
However, we aren't diving. Since nitrogen is denser, it makes the wheels heavier, giving the bike slightly less performance.
Cons of filling tires with nitrogen:
I wouldn't bother, it's up to you though.
The journey is the destination.
2006 VN750 (SOLD)
Red spark plug wires
Stainless Steel brake lines
Stiffer fork springs
Givi bags, Wingrack mount