I’ve been asked whether there should be one or two spaces after the period in a sentence. Today the rule of thumb is one.
Why? Two spaces were mandated in a typewriter world, which had non-proportional type and no bolds, italics and the like. Now that we have proportional fonts and formats, the double space after the period is not needed for clarity or ease of reading anymore. And using one space can help make the copy look professionally printed.