I have to wear goggles, when you get going a certain speed, you can't get away with squinting. In order to stay in control, you have to be able to see. I have tried to not wear goggles, it just dosnt work.
Probably the only time you won't need goggles IMO is on the bunny slope learning to snowboard. And thats if there's no sun, rain or snow falling.
Otherwise yes, I remember being a novice rider and my friends of course took me to the top of the mountain and I had a pair of cheapo goggles. They fogged up and I tried wiping them but it kept fogging up. They passed me 4x when I was trying to make it down once. I couldn't make it 30 yards without tears forming and icing and the pain was horrible.
Definitely wear goggles for all the reasons listed above, and I wouldn't recommend sunglasses for a beginner. I see a bunch of people on the greens biting it hard all the time. If you fall, sunglasses can fly off, or worse case scenario, break on your face if you faceplant.