Concept art

Concept art is used in the planning stages of a game, this can be used as a suggestion to a high ranking designer for opinions on an initial design to help cut down costs of modelling and reduce the chance of  it being rejected. This can also help people such as texture artists prepare textures for the model when it comes to putting the textures on.

These can be added to special edition sets to give the consumer a little extra for their money. Concept art can also be used in posters as a marketing material.
This example is a Terantatek from the game Star Wars: The Old Republic. As you can see this has been drawn to show the motion of walking as well as the overall design of the creature, this will then help the designers and animators to create the creature as imagined.