Why 3D print lenses?

3D printed lenses bring the eyewear market an amazing capability: unique products and lens customization.
But why do they make sense?
In a nutshell: 3D printing allows for unique customized lens designs which is what prescription eyewear is all about. In addition with 3D printing you will be able to finally add "smart" to prescription lenses or add prescription to all these cool goggles that are coming out.