In Sketch and Toon, there is a balance to strike between which settings to change in standard materials, which to change in sketch materials, and which to change globally. Almost any setting can be changed at either a global level or a material level. Which one you change on a case-by-case basis depends on the style you're attempting to create. If you're working on a technical diagram and attempting to create a hand-drawn colored pencil style, you will most likely want to create a number of different sketch materials. If you're creating a cartoon, you may want everything to maintain a consistent black outline and color your objects through a series of standard materials.