Think of situations in which a font has a single case. Like say on calculator-like displays which have additional elements to show letters. You could see those

Think of situations in which a font has a single case. Like say on calculator-like displays which have additional elements to show letters. You could see those on old VCRs for example: https://i.imgur.com/aloDSQh.jpg https://i.imgur.com/aloDSQh.jpg Notice they're uppercase. Now imagine this display but with lowercase letters: 1. In most letters the top half of the letter display is not used, but in some it is. 2. In some letters like "q y g j" you need a "descender" (https://en.wikipedia.org/wiki/Descender https://en.wikipedia.org/wiki/Descender), which means you need to extend the display further down, and add more elements. 3. Digits themselves are "capital only". There are no "small case" digits in most fonts, or in writing. Which makes capitals consistent with them. So capital letters are simpler, more visually consistent and as a result also I'd say more legible on displays where there's not a ton of text to begin with. Even on pixel displays where the "descender" or "unused top half" is not a technical problem, you still would need larger spacing between lines to fit the descender without some letters touching the line below. Capital-only is also the optimal choice when you need to print some small label on a device, or on a street sign, for example. It's a "STOP" sign, not a "stop" sign. No one does "small letters only" labels. It's either capitals only, or mixed case. TLDR: Capital letters FTW.