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I still find people who do this
(slrpnk.net)
At my last job, a bunch of the older folks did not realize they had a "two spaces" habit.
It's a clear tell.
Saw this meme and thought I'd point that out.
I imagine because it's larger than the space between words (one space), so as to indicate a break in thought, but not long enough to cause the reading to be stilted.
But if you're ee cummings, go right ahead...