But you've seen it before, and if you saw it again and you didn't remember exactly what the symbol stood for, you would probably still remember it was math related, and be able to look it up fairly quickly. There's a whole class of domain symbols that fall into this category, and even for the people that don't know them immediately, if they look them up, they might find useful info that conveys some of the original developer's intent. For example, Δ, an searching for it will probably bring you to Wikipedia[1], where some common usages are easy to see (and "change" is the top one, which is what I would assume when seeing it).
Increased symbolism front-loads learning to increase expressiveness later. If we've already front-loaded that learning to a small or large part on a large chunk of the population, that can greatly change the equation for how much it slows initial understanding of the code, and thus it's usefulness. As I mentioned elsewhere, we generally use '+' and '-' in programming languages because everyone already knows what they mean. We could just as easily use add(a,b) and subtract(a,b), and in some languages we do so, but in general there's so little friction in using the most basic math notation it's accepted without qualification as a better way to do it.
Increased symbolism front-loads learning to increase expressiveness later. If we've already front-loaded that learning to a small or large part on a large chunk of the population, that can greatly change the equation for how much it slows initial understanding of the code, and thus it's usefulness. As I mentioned elsewhere, we generally use '+' and '-' in programming languages because everyone already knows what they mean. We could just as easily use add(a,b) and subtract(a,b), and in some languages we do so, but in general there's so little friction in using the most basic math notation it's accepted without qualification as a better way to do it.
1: https://en.wikipedia.org/wiki/Delta_(letter)