One or two spaces after a period? How about three?
widespacer.blogspot.comI’d always heard it was to try to minimize rivers in text. I don’t see that mentioned.
Check this out: http://widespacer.blogspot.com/2012/12/a-river-runs-through-...
They don't mention it here, but I think they might on a different post? Rivers are going to show up more in a monospace font (which your link points out), so that would make sense. With modern fonts it makes sense to be putting the spaces in after a sentence stops for readability though. Microsoft word allows for manipulating spacing anywhere there are still rivers.
I've always been annoyed by the way html treats whitespace. Having more space between sentences is so much more readable.