The line height issue comes, somewhat, from the argument about textual color. If you have no leading at all, the text ends up very cramped and dark which is con

The line height issue comes, somewhat, from the argument about textual color. If you have no leading at all, the text ends up very cramped and dark which is considered very unfavorable. For instance, I'd bet you'd be hard pressed to find many books printed professionally which don't have at least half a line of leading. How leading affects someone's ability to scan lines, I don't know so much about. In my experience, medium text color is more pleasing to read in general -- I feel less eye strain, less cramped -- but I don't experience much difficulty following lines regardless of leading.