That line length should be restricted in body copy is a universally accepted principle among typographers [0], and has been for a very, very long time. The reas

That line length should be restricted in body copy is a universally accepted principle among typographers [0], and has been for a very, very long time. The reason is a practical one: when line length passes a certain point, it is harder for the eye to track from the end of one line to the beginning of the next. Typographers may take more creative liberties when it comes to other bits of text, but for body copy where the reader will spend several minutes or even hours of time, legibility and reading comfort are top priorities. This is why printed text with smaller type or larger paper will almost always employ larger margins, multiple columns, or both. In print, when a high per-page word count is desired, multiple columns is a go-to solution. But multiple columns for body copy is awkward on the web, since we're used to scrolling vertically—and real estate is free. So the best solution in most cases is simply to add margins. [0] I like to point people to Matthew Butterick's excellent (and free) Practical Typography (https://practicaltypography.com/line-length.html https://practicaltypography.com/line-length.html), but any introductory typography book will have a section on line length.