knife should be able to make similiar filings...
No argument here. But there are a couple things the sharpener seems to do better than the knife. For one thing, I find it a lot quicker to generate uniformly thin shavings. Second, it seems to be much easier to keep the shavings confined to one spot. I mean, if it's windy, you can hold the sharpener in one hand turned so the shavings stay in your hand. YMMV.