I worked (very part-time) a typesetting job for 10+ years. We were making a journal with (sometimes) pretty narrow columns. Microtype was surprisingly helpful

I worked (very part-time) a typesetting job for 10+ years. We were making a journal with (sometimes) pretty narrow columns. Microtype was surprisingly helpful, while remaining (almost) invisible to a layman's eye. (Once you know about it, you can spot the differences in letter widths sometimes.) Interestingly, Guthenberg used very similar techniques with varying the shapes of letters so that the "blackness" of the page could be more uniform.