Very little (I rarely make peanut butter, but I roast hazelnuts and make homemade "Nutella" with dark chocolate). Out of about 900 g hazelnuts (minus a bit of "shrinkage" because warm roasted hazelnuts are delicious) and 70 g dark chocolate (Costco Suisse Delice) we get about 850g or more of blended hazelnut chocolate goodness.

Add some almond milk and other stuff to the Vitamix and you can make a really nice power shake from the residue, and lose only a few grams to the soap and water cleaning required.