Often times when a client is trying to select wallpaper, they get only a single iteration of the pattern, sometimes not even full-sized. Many quality suppliers will be able to provide a photograph of a room with the wallpaper in use - but even then, usually only in one particular color even if the style comes in many colors.
A combination of GIMP/Photoshop, and 3ds Max can give a client not only a good idea of how the wallpaper will look in use, but how it will look in the particular room and location they want it.
Sunflower Ogee
One of my first 3D renderings for a client on the left, the finished
room on the right. The furniture and wardrobe were all custom
designed by Brendon Koo of Brenko Design.