[jack_jennings]

Not an easy phenomenon to describe or even illustrate. I believe that some legibility come through slightly uneven textures that are created by varying shapes that words create and the "color" (density of light and dark) that is created by different sequences of letters. Different words become identifiable by their shape and the visual space they occupy. Kerning somewhat counteracts this by attempting to make sequences appear more regular, so "robotic" kerning, might be described as an extemely even appearance to the detriment of legibility.

Granted were talking about a very micro adjustment. In the end he word will still be word and will still be read.