My pal Watts Martin has a post that explores an artifact from the past: the insert key. Martin, who’s been a Mac head much longer than I have, remembers when Mac keyboards still had an Insert. They no longer do, of course, but my Unicomp Model M clone does as do several other PC keyboards. The key was used to toggle between inserting text and overwriting it. Emacs calls the latter overwrite-mode.
The idea of insert mode is that text in front of the cursor is pushed ahead as new text is added behind it. When insert mode is off—that is, when overwrite-mode is active—the text in front of cursor is overwritten. Overwriting text used to be more common but these days everyone uses insert mode and you rarely see it.
Still, as Martin says, overwriting can sometimes be useful and if you have an Insert key there’s no reason not to use it in Emacs. That’s a one liner and easy do in your init.el. On the Mac, the Insert key is usually mapped to Help but on other systems it probably has a different mapping so you may have to experiment to discover what it is.
Finally, Martin wanted a visual clue as to which mode he was in so he changed the shape of the cursor to reflect the mode. Again, that’s easy to do. He uses overwrite-mode-hook to toggle the cursor shape.
While I agree that overwrite-mode can occasionally be useful I don’t—and have never—used it enough to dedicate an actual key to it. I’m perfectly happy to simply call overwrite-mode to turn it on and off.