Spheres of Influence, by Cycling Magazine

Sphere of Influence

Here are some highlights from the article:

High-quality ceramic balls are ultra-smooth, resulting in a bearing with very low coefficient of friction.
Low friction leads to a longer lifespan.
Ceramic bearings need lubrication. “A high-quality ceramic bearing will work better than steel in the absence of lubrication and have a longer lifetime than a low-end ceramic, but if you want the most out of your ceramic bearing you must lubricate them,’ says Martin Banke of CeramicSpeed.
High-quality ceramic balls are very stiff so don’t deform as much under load as steel, which improves resistance to wear and increases stiffness in the entire system.
Ceramic balls are lighter than steel equivalents.
While the overall weight difference it makes to your bike is negligible, lighter ball bearings spin faster, reducing friction and improving rolling resistance.