Oh, man, the number of times I’ve used that principle, ucb, since learning it, as a wee young 'un.
I used simple math to figure if the new bookshelves would hold the excessive number of DH’s (at the time) boxed books. I use it to track the degree of inclines in my biking path and project the effort based on the length of the slopes. (Really, to pick the easiest path.) I needed to figure how much dirt to fill the new planter box (large, on wheels) - and how large that box could be before the weight of the dirt meant I couldn’t move the box. Not to mention cost calculations for size and how to cut the wood lengths just so, to avoid buying even one excess piece. Fun thread.