Matthew, MS Word’s special characters include “Em Space,” “En Space,” and “1/4 Em Space.” I assume they are spaces the width of an m, n, and 1/4 m, but why would I use them?
They´re used as lengths for indent & exdent. The Em provides a proportional lenght for it. It is commonly accepted that the longer the width of the text, the indent has to be larger, so it´d make sense to use the “En Space” for shorter lines of text and 1 o 2 ems for longer ones. Keep in mind that you can set the paragraphs without making them to start in the next line. A new paragraph may start in the same line as the last one, so in this case, it´d be really helpful to to insert a special character equivalent to an em and distinguish the different paragraphs.
It’s confusing terminology, but “em” and “en” do not refer to the letters m and n. Rather, the em is a space equal to the point size of the font; the en is half that. See also. So if you’re setting type at 10 point, the em space would be 10 points wide, the en space 5 points, and the 1/4 em 2.5 points.