I recall reading somewhere that in typesetting the goal is to have 10-12 words / line because that is how much of a line the eye reads without side-to-side scan

I recall reading somewhere that in typesetting the goal is to have 10-12 words / line because that is how much of a line the eye reads without side-to-side scanning. Personally I find that with long lines I often waver to a different line as I scan from left to right. Thus I need to re-read the line which otherwise I would have read in a single pass.