Slate Magazine on the reasons why you shouldn’t put two spaces after a full stop. I used to have this habit myself, having taught myself to type on a typewriter (yep, I’m that old).
Still others said they used two spaces all the time, and they were thrilled to be so proper. When I pointed out that they were doing it wrong—that, in fact, the correct way to end a sentence is with a period followed by a single, proud, beautiful space—the table balked. “Who says two spaces is wrong?” they wanted to know.