Most books aren’t printed on 8 1/2 x 11 paper so why are these the standard paper dimensions? Paul Stanley offers an answer:
…we have ended up with paper sizes that were never designed or adapted for printing with 10-12 point proportionally spaced type. They were designed for handwriting (which is usually much bigger) or for typewriters. Typewriters produced 10 or 12 characters per inch: so on (say) 8.5 inch wide paper, with 1 inch margins, you had 6.5 inches of type, giving … around 65 to 78 characters: in other words something pretty close to ideal. But if you type in a standard proportionally spaced font (worse, in Times — which is rather condensed because it was designed to be used in narrow columns) at 12 point, you will get about 90 to 100 characters in the line.
The standard paper dimensions are thus not optimized for reading using printed fonts so typographers try to make adjustments. One adjustment is to abandon the standard paper size which is what books do. Another is to make the margins very wide which is the Latex default.
[Another] answer — which is what most wordprocessors did — was to stick to the standard “document design” (margins of an inch or so) and just use proportionally spaced fonts as if they were typewriter text. This produces very long lines, which are not comfortable to read. But that discomfort can be somewhat alleviated by increasing the space between lines (1.5 or double space), which helps prevent “doubling”, and by avoiding type sizes below about 11 or 12 points (depending very much on the design of the font).
Another possibility is to use the margins for marginalia, which I like. (Stanley points to the Latex tufte class as a way to do this.) One could also a two-column format or just make the text bigger.
These are all potentially valid design choices. I happen to think that the most conventional one (stick with 1 inch margins, and add line spacing to prevent doubling) is probably the worst of them, and that it only seems “right” because we are accustomed to it. And it doesn’t generally save paper, because unless you use single spacing you lose vertically the extra space that you gain horizontally.
We need to fix this problem. Now is the time for a margin revolution.