The knife edge crank main purpose is to swish through the oil in the sump easier resulting in less load on the engine, the other major result is the reduced rotational mass of the crank form removing the metal to reshape it which helps the engine accelerate quicker. Some people are all for them but others don't see the benifits. I probly wouldn't go to all the way on a crank if you want it to last or if your an engine breaker but definatley getting a mild lightening and reshaping wont hurt it if your going to race or whatever