The system fonts Courier, Menlo, and Consolas are examples of
The samples above are set at the same point size. But the monospaced font, Triplicate (first and third rows) takes up more horizontal space than the proportional font, Valkyrie (second and fourth rows). The differences are most noticeable in characters that are narrow in the proportional font (like f i j l r t) and the punctuation characters.
Monospaced fonts were invented to suit the mechanical requirements of typewriters. They were not invented to win beauty contests. Compared to proportional fonts, monospaced fonts are harder to read. And because they take up more horizontal space, you’ll always get fewer words per page with a monospaced font.
In standard body text, there are no good reasons to use monospaced fonts. So don’t. Use proportional fonts.
Do you need monospaced numerals—typographers call them
tabular figures—so that columns of numbers will line up? This is such a common need that most proportional fonts include tabular figures by default. See alternate figures for how to verify this.
Do you need to quote software code or HTML in your document? Then use a monospaced font for one of the reasons software engineers do—software code includes compressed syntax like (int i=1; i<111; i++) which is more legible when set in a monospaced font
(int i=1; i<111; i++).
If you really do need a monospaced font, the Courier system font is one of the worst. See Courier alternatives.