The only two advantages that folders have (that I can think of) are legality and compactness. In some states like mine, a fixed blade of any length must be carried openly, while it's legal to carry huge folders concealed. So while an Izula does like an ant if laid next to a Cold Steel Voyager X2, its the X2 that's legal to conceal. And as far as compactness goes, if a guy wants more "reach" for whatever reason, a folder will obviously be around half the length of a fixed blade of comparable blade length. A trade off, but one that many folks seem to accept.
I have a question for anyone who uses a pocket sheath. Have you ever accidentally cut your pocket or other clothing while drawing or holstering your knives? I like the idea of a pocket holster, but they seem oops prone. I've never tried one though, so that's why I'm asking.