Extra spaces between sentences added readability in the time of monospaced typing (where every letter took up the same amount of space). Few fonts in the digital era follow this spacing style; ergo, the two space necessity has been dropped.
It’s true. Today, most publishers – both print and online – use one space between sentences, and we recommend that you do too. This is especially significant on webpages. Web copy should be direct and concise. Extra spaces clash visually and philosophically with this tactic.
Some writers follow this old rule out of habit; others because they had teachers who taught this form long after typewriters were put to rest. But it’s time now. Typewriters are gathering dust. Don’t let your writing follow suit. More