Or those of us who learned to type back in the days of Ye Typewriter.
It's supposed to be an em-space, not two normal spaces, but that is hard to to in ASCII.
vim does it by default (eg. when rewrapping a paragraph). I only recently discovered the nojoinspaces option to turn it off. Before that I was removing the extra space by hand all the time.
Say it ain't so...
:%s/\. /\. /g
It's not worth typing all that to remove one extra space.
"/ ^Mx" is easier.
the command gJ does a join without the space logic.