I found this argument in favor of two spaces after a period. I favor the single space, but not for any of the reasons he explained.
I’m also not a graphic designer. I had to take a couple of classes on design and layout, and I was competent. But mostly efficient. I was known for being the first one in the room to finish a design, and it would always be at least middle-of-the-pack. On a tight deadline, I was the guy you wanted finessing QuarkXPress.
You see, I’m also a full-justification guy. And if you put a single space in front of a period, then the typography engine can put more space after a period if it needs. I suppose an intelligent engine could remove the double space if it needed to gain a half space, to get a better fit, but not all of the engines will. I find I get better results if I put a single space in and let the computer do the work.
So, if you’re wondering, that job I had where I had to put two spaces after everything because of tradition, and for no other reason… Yeah, that bugged me. I always did a find and replace just before submitting the document.