The biggest advantage of A4 isn’t explained clearly: since it follows √2 ratios, you can reduce by half and get it to fit exactly 2 pages of information on 1 sheet, so you can make any document into a 2-per-page booklet with perfect formatting.
If you try to print 2 pages per page with US Letter, you get massive waste and it looks terrible.
The biggest advantage of A4 isn’t explained clearly: since it follows √2 ratios, you can reduce by half and get it to fit exactly 2 pages of information on 1 sheet, so you can make any document into a 2-per-page booklet with perfect formatting.
If you try to print 2 pages per page with US Letter, you get massive waste and it looks terrible.