Most designers use illustration tools to draw diagrams, but some designers work on User Interface (UI) and User Experience (UX) design as well (especially for mobile and browser games). Sometimes, even more complex illustration tools can be used to draw infographics or to give a particular format to a GDD.
Illustration tools are also used to explain some mechanics that require a visual explanation. Designing actions that a character can perform in an action game is a good example; it’s always a good idea to pair a textual description with an image.
Creating wireframes and click dummies is another important part of writing GDDs. A wireframe is essentially a sketch of the UI layout, made only using boxes and basic lines/shapes, ...
