Visual hierarchy refers to the arrangement of elements, including text, to help users navigate a page. In other words, it helps you tell users where to go to find the relevant information using methods of size, color, contrast, alignment, negative space, style, etc.

Knowing the hierarchy within a page, you can decide how many typefaces you need, for example, one typeface for headlines and subheads and another for body copy, captions, button labels, etc.

Users tend to see large-sized letters in a different typeface and weight and assume it's a new section or a vital piece of information. So variations of typefaces, weights, sizes, and spacing between text elements can help designers set zones of importance (aka anchors), to increase the scannability of a page.