The 3/4 face is a useful skill for any cartoonist. it means you are able to see both eyes, and so a large range of expression, but the face is angled to point left or right, so it can face, or face away from things. A lot of cartoonists, however, almost always use the 3/4 face: if two people are shown facing each-other they will be shown in 3/4 face - which actually means their lines of site are at 90 degrees to each-other.
This trope is for when the 3/4 degree face is used far more than would be applicable by any normal laws of perspective. It therefore only applies to 2D drawn media like comics, 2D animation and 2D video games. It particularly applies if characters are only seen from the exact same 3/4 view.