The pyramid fans will tout the fact that thickness taper remains constant from handle to tip on a pyramid profile, where on a parallel profile, the thickness tapers the length of the limb. Therefore less guess work on a pyramid. On tree stave bows specifically, I'm not sure it works like the theory suggests. You still have to scrape the flat spots and get the tiller correct either way. Roughing one out may be easier on a pyramid, but finishing them requires the same amount of skill and effort, so far as I am concerned.