So whenever you consider how a user would feel using the end product — frustrated or satisfied — whenever you choose ease of use from point A to B over flashy design, anticipate pain points, or add in accessibility, you are practicing good UX.
We’re focusing on legibility instead of readability. There’s a difference. If text is legible, it doesn’t mean it’s readable. With legibility, text can be interpreted, but readability takes it a step further and incorporates the emotional effect of design with the amount of effort it takes to read. This is why smaller body text sizes thought as “legible” are considered sufficient.
But in actuality it’s not the size that causes that perception, it’s the style of the typeface; its design nuances, kerning, letter spacing, line height, and other attributes that affect our visual interpretation. Some typefaces just don’t look quite as appealing when big.