Sometimes it is handy when doing something like ASCII art or drawing ASCII diagrams. Imagine editing a much more complex variant of this

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  | AB |
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Finally, Shift-INS pastes from clipboard on Linux. A keypress saved compared to Control Shift V in a terminal. However they don't paste from the same clipboard: one is the primary selection (middle click) the other is the actual clipboard. However when I Shift INS into this textarea on HN I paste something else so I don't really know the rule and I stop here.

I always use middle click, which is a hardware button below my touchpad and it is one more saved keypress.

I use it quite regularly in text editors, in particular when authoring something with two-dimensional layout (simple diagrams, folder-like line trees), and occasionally for the CUA Cut & Paste shortcuts (e.g. in terminal emulators).

There’s also a number of applications where it has a useful binding, such as marking a task as (un)complete in Outlook, or (un)flagging an email.

My keyboards have always had an INS key but they’ve never done anything and I’ve never bothered to map them to anything. I do sometimes want to overwrite, but that’s always in Vim where I can enter replace mode.