The terseness is useful not just for writing, but also for reading. In maths, the shape of a formula is often more important than what each symbol in a formula “means”. The terse notation allows you to quickly grasp the shape and draw parallels between seemingly distinct areas of mathematics, as well as transform the shapes in your head without being bogged down by whether A is a matrix, a real number, a function or whatever.

When I code, I prefer comments explaining the general idea of what’s happening and why in a given folder/file/section (not explaining each line) combined with terse code.