My first thought is why are you not eating them? Watching cholesterol? watching fat/calories?
I personally never toss the egg yolks. They're factored into my diet and there's a lot of good stuff in the whole egg. I'd rather eat one or two eggs vs. 5 egg whites and you get a lot more protein and nutrients that way. In fact, my nutritionist recommended that I bump up my current eating plan with at least 3-6 whole eggs per day.