Do not use fonts other than XXX. Some companies has designated fonts for brand consistency.
The chosen font may also be a font that has been specially designed for screen readability, with generous spacing and width. And some are common fonts that can be found on most modern operating systems, which means it is less likely to be substituted with a default font, if not found on a user's computer.
Such as Sans serif fonts display well on screen and are more legible than typefaces with serifs, which can appear pixelated or blurred at small sizes.
The checkpoint examines the entire HTML source code of a page and reports if within the (font(-family)) tag, the specified font (i.e Arial) is not found.