You just helped me much more that you could have guessed: see, they talked about agendas. And it just occurred to me that the folding method devised by the OP yields a 7×5 grid, which is exactly what I need to fit a month worth of agenda. The squares are relatively small, but they suit my needs.

So, an A4 sheet of paper is worth 2 months of agenda. 6 will last me a year.

I'm too lazy to buy an agenda, but now I have one. Thank you.