Comment by saalweachter

That's not a difference between ANSI and ISO paper sizes.

ANSI A (US letter) is a half sheet of ANSI B (ledger/tabloid) is a half sheet of C is a half sheet of D is a half sheet of E. When producing the paper, there is no waste of material or time, its the same process just starting with a slightly differently sized starting sheet (hypothetically; I am assuming that paper production has advanced beyond shaking screens of the largest handleable size by hand).

The difference is that ANSI A, C and E have aspect ratios of 17/22 (0.77) and ANSI B & D have aspect ratios of 11/17 (0.65), while all ISO sizes have aspect ratios of 1/sqrt(2) (0.71).

The waste comes in when scaling between adjacent sizes.

Going from A4 to A3, you can enlarge a document to 141% of the original size, and the margins will match.

Going from US letter to tabloid (ANSI A to B), the width of the paper is 129% larger and the height is 154% larger, so you can only enlarge your document to 129% the original size, and you have larger vertical margins, which is waste.

(But if you double it, from A to C, the problem goes away, because the aspect ratio is the same; so you can produce posters of multiple sizes, just not on every ANSI paper size at once.)