A single bevel grind can allow for a much, much steeper angle at the edge and the blade can just glide through the material. A lot of those single bevel knives are intended for very specialty cuts, rather than as a replacement for your regular chef's knife. Here's a demonstration of using a yanagiba, which is more of a sushi knife. Note that the cut itself is intended to be made at an angle. If you take the same knife and start chopping carrots and onions with it, you'll probably find your cuts naturally want to curve. It works great for this particular way to cut sushi, if you know how to use it, but not so great for general purposes.