Well, it's meaningless on this board, since multiple spaces are condensed to one no matter what. I think it irritated someone a while back that their monospaced doctrinaire dinosaur-typography wasn't being respected by the software, which has the audacity to conform to those newfangled 1980s-era typographical styles.
See? Two spaces between sentences here, while there was one up above. You should still see it if you quote the post, but reading it normally, it'll show up as one.
And three! Let's just be completely crazy! And let's get some em-dashes— like these— in the mix, as well! I love me some em-dashes.
See? Two spaces between sentences here, while there was one up above. You should still see it if you quote the post, but reading it normally, it'll show up as one.
And three! Let's just be completely crazy! And let's get some em-dashes— like these— in the mix, as well! I love me some em-dashes.
. More seriously, I don't know where the UK stands on this. Maybe the two-space is an English-speaking thing and includes Britain, Canada, Australia, etc; or maybe it's just the US. I'll wait for Brits to chime in.

The first high school I attended had those monstrously big manual typewriters that required every ounce of strength to use, and when I moved to a high school with electric typewriters my teacher yelled at me for pounding the crap out of it. It took a few lessons to get out of that habit.