> There is a good reason to use two spaces, and that is that when you're typing, you're only creating text, not typesetting. Software does the typesetting now, and will automatically space out sentences in a way that looks right. Furthermore, it is easier for software to detect two adjacent space characters than to guess at where you meant to put a space at the end of a sentence and where you meant to put a space after an abbreviation. You don't need to change your habits, because computers work for you, but using two spaces between sentences helps them do their work sometimes. Also, many people still use monospace fonts for many purposes.

improved version