Although I don't agree with the width statement, I just wanted to note that I personally find the B sizes nicer than the A sizes for non-fiction books. I find A

Although I don't agree with the width statement, I just wanted to note that I personally find the B sizes nicer than the A sizes for non-fiction books. I find A5 pages a tad small for textbooks, but B5 seems just right. (So, effectively "B4 folded", which is usually printed on A3 to begin with, then folded into signatures, bound, and then ultimately cropped.) And since it's all the same proportion, it makes it easy.