It's all about communication. Creating a clear, unambiguous portrayal of a product so that informed decisions can be made.

Some types of visualization include:

Thumbnail sketches:
a thumbnail sketch is is the most basic drawing type. It is drawn quickly by hand with basic tools (Pencil, pen, marker) and its purpose is to communicate a general idea. It is not meant to define in real terms or units, however this type of sketch often includes notes, labels and symbols.

Diagrams and Charts:
Visualization often requires the communication of information that is not physical in nature. For this type of information, a presentation including Diagram or chart information helps to convey the idea.

Storyboards:
Storyboards are particulary helpfull when the information you are trying to convey is process or sequence related. These visuals can be sketchy or photorealistic. Formatted in comic book style, with cells containing discreet steps in a process, storyboards are often used to show iinteractive screens, articulating components or assembly and manufacturing steps. More recently, due to the availablity and affordability of animation programs this type of visualization is done via computer. Animations can be cartoonish or photorealistic. They can also be done with live video footage.

Hand drawn Renderings:
Hand drawn renderings have been traditionally used to communicate aesthetics. The power of these visuals is in expressing emotional and sensual characteristics of a design. Excitement, power and quality are just a few of the attributes that can be conveyed.

Computer generated 2D renderings:
Like hand drawn renderings, these visuals also address the aesthetic, emotional and sensual characteristics of a design. In addition, Computer generated 2d drawings add a level of precision and can leverage the drawing into the design process as templates and guides to the 3d cad process. Some computer programs include Photoshop and Illustrator.

Computer generated 3D Photorealistic renderings:
This type of visualization is the most descriptive and realistic form as the information developed is digital and can be used downstream to generate Industrial designs and visuals for pre production purposes.