In the nineteenth century, which was a dark and inflationary age in typography and type design, many compositors were encouraged to stuff extra spaces between sentences. Generations of twentieth-century typists were taught to do the same, by hitting the spacebar twice after every period. Your typing as well as your typesetting will benefit from unlearning this quaint Victorian habit.

Robert Bringhurst, “The Elements of Typographic Style”

Hear, hear!