[0] http://www.phonearena.com/news/Hitachi-unveils-4.5-inch-3D-d...
Microlenses also enable stuff like light field cameras and light field displays. Particularly cool in this area is NVIDIA's near eye light field display[0].
However, for a applications like this you don't really need 3d printing, one can make microlenses for these systems with molding.
However, there is one application that might benefit from 3d printing micro optics. Augmented reality contact lenses[1]. You can't just put a bunch of LEDs on your eyeball and expect to see anything, you need optics to focus them. One could make microlenses as before, but now we can print an array of them that has a bunch of holes in it so your eye can breath. Alternatively, we can make a complicated weave like structure of light pipes with lenses on their ends that lead to LEDs on the periphery of the contact so that we don't have to worry about making transparent LEDs and wires.
[0] https://research.nvidia.com/sites/default/files/publications... [1] http://spectrum.ieee.org/biomedical/bionics/augmented-realit...