It may seem a little silly to call fat marker sketches a technique or a tool. The reason for calling them out is we too easily skip ahead to the wrong level of fidelity. Giving this rough early stage a name and using a specific tool for it helps us to segment our own creative process and make sure we aren’t jumping ahead to detail a specific idea when we haven’t surveyed the field enough.
We don’t want to make our early UI flow look too finished. We need to leave room for UI design.