A good serrated edge will cut through practically anything, it bites in and guides a pushcut, rips or saws through tough stuff, and will handle these specialized tasks better than a plain edge especially when the edge is dull or damaged. A plain edge cuts clean, can slice through softer materials easily, generally offers better control and is easy to sharpen or repair, but takes more length to slice as deep as serrations. Even gut hooks have their place, strong, inexpensive, good for cord, safer in tight confines, gives good leverage to pull through tough fabric. Each has their place, and depending on the job, each can perform where the other designs are not ideal, I use each in one way or another, and sometimes end up carrying more than one blade. IMO most folders are too short to use more than one type of edge, but larger fixed blades can make use of both.