What difference does it make what font a website uses? I get having a monotype, a serif and possibly a sans-serif, obviously setting the font size should be a t

What difference does it make what font a website uses? I get having a monotype, a serif and possibly a sans-serif, obviously setting the font size should be a thing, but the actual font? I just don't see what difference it makes if a website is in Helvetica, Times New Roman or Arial. If one font is easier for me to read than another I can chance it in my browser, which makes more sense than letting some web designer, who's more focused on brand identity, pick a font for me. There might be some cases where you really wish you could pick a specific font, but you can't really use it to convey meaning anyway, because that would not work for screen readers or people who chance the font on their system to help readability.