[gucci-on-fleek]

My guess would be that this was designed to be printed on smaller sheets of paper, like used in paperback novels and similar. But for some reason (possibly to make it more convenient to print on standard paper), the PDF was produced with Letter dimensions.

I don't think that it's for taking notes like the other reply [0] suggests, because if that were the case, I would expect for the cover to take up the whole paper width (since nobody would ever take notes on the cover), and I would expect the margin width to alternate between pages (since it's really hard to write on the inner margin in a bound book).

Using the example given in the other reply [0], the SCOTUS opinions are so narrow because they're printed on a bizarre paper size of 6 1/8" by 9 1/4" [1] [2], not to leave room to take notes.

[0]: https://news.ycombinator.com/item?id=46887595

[1]: https://www.supremecourt.gov/casehand/guidetofilingpaidcases...

[2]: https://www.supremecourt.gov/filingandrules/2023RulesoftheCo...