Certain processes will only cut certain types of materials. For example, oxyfuel can only cut carbon steel, plasma can only cut electrically conductive metals, while a waterjet and laser can cut a range of materials.
Certain processes excel at different thicknesses. Generally, laser is most frequently used to cut thinner materials, plasma is used for mid-range to thicker materials, and oxyfuel is used for very thick carbon steel. Waterjet can cut across the thickness range.