Originally Posted by crash1369

The main benefit to filling your tires with nitrogen is that it is lighter then air, which is supposed to increase your gas mileage. But as mentioned it also does not leak out as fast, there is also less affect from varying temperatures which means your tire pressure will remain more consistent. If you can get them topped off with nitrogen for free and without to much hassle you might as well it's certainly not hurting anything, but again regular air is largely composed of nitrogen anyway and there is no harm in "mixing" them.