The problem with using SiC powder as opposed to a diamond plate, is flattening becomes a separate process, and combined with the setup, mess, etc.... something you're less likely to do. As opposed to a diamond plate, where, you can easily maintain the stone in just a few seconds, anytime during sharpening, with basically no setup... so you're more likely to keep the stone "tuned up", fresh, and ready to go. You'll also have less chance of contaminating your sharpening stone, and get more predictable results with a diamond stone.