By golly there IS such a thing as a "pants-putter-downer" on YouTube!
https://www.youtube.com/embed/BDQ0UUZ0k50

E) Why can't we give up FISH for lent?
(personally, I love fish)

It a quick and dirty way of adding emphasis to what you are saying. Like italicizing ing ing (that would be looking at something slanted three time normal italics) or Underling ing ing (Word with three lines under it) Have you got that all straightened out better-er-er now?

As typewriters came into common use, I can't see how the mechanical versions would allow letters to overlap. They are designed to strike and advance to the next space.
Backspacing to over-strike a character is simple enough, but generating 1/2 space overlap consistently? tricky at best.