Single coated lenses are in principle technically inferior as they are more prone to light loss and multiple reflections, manifested as ghosts and scattering (hazy) light. These problems are more pronounced in scenarios with brightly lit subjects or where there is light extraneous to the required illumination of the subject (e.g. a backlit scene). More highly spaced modern optical systems are usually fully multicoated, which means every optical surface has multiple layers of very thin transparent materials deposited on them (such as MgFl) which enhance transition of light and suppress internal multiple reflections (which lead to ghosts and other problems).
Many vintage camera lenses have only one coating, typically on the first optical surface (the front face of a camera lens for example), and it is a single layer coating. This is because coating technology was more challenging when it was first being implemented on an industrial scale in the post-war era. This however still notable enhanced the throughput of lenses and suppressed other undesirable optical artifacts. As time passed, many artists became attached to the "look" of simply coated or even uncoated lenses. The latter consideration is what has motivated Voigtlander to make single coated lenses (if I understand them, and I think I do).
Voigtlander has a penchant to deliberately replicate history with camera and lens technology, which overall I think is a good thing. However when it comes to coating technology, I personally, don't buy into the single coating idea, but each to his own.
