Being lighter is huge for snowboarding. I think back to when I was overweight and how much harder of a time I had controlling and throwing the board. Being agile and lightweight improves your riding so much, and also makes you more resistant to injury.
I suppose being 10 pounds lighter might make you fly .5" higher than my bulky 5"11 205 but "throwing the board" is easier as a lightweight? mmmm I'll most definitely disagree with that opinion.