A new 3D print service has launched, SnapilyPro, but it's not what you think: they print 3D models in 2D.
The service accepts 3D photoshop PSD files and uses lenticular printing to produce a flat surface image that appears to move when you rotate the image.
Why would you use a 2D print service when you really want 3D? Perhaps you want to produce mailable samples of a model before committing to actual printing, which would be quite a bit more expensive. For example, Snapily will produce a 5x7 inch 2D image of your 3D model for only USD$12, and there are substantial volume discounts.
Another potential 3D application is as an adornment for a 3D model. One could imagine using lenticular elements as "windows" on an architectural or vehicular model when it would be difficult to properly finish an interior portion.