A reader commented on our post about how to turn off overtype in Word:
“Just what is the Insert Key for, anyway? I have hit that INS key more times than I could ever count and not for the intention it was put there for! It’s SO aggravating to be typing away, not realizing you were losing faster than you were gaining. And just what IS the intention for that key anyway? If I want to insert anything, I can just place my cursor in that spot and type what I wanted inserted.”

Basically that key exists to turn overtype on and off. Overtype is when you type over and replace what’s written on the page. Insert is when you add to it and move what comes after it down the page.
There are some times when typing over things might be preferred. The Insert Key is also used for keyboard shortcuts in some programs.
Remember, if you accidentally turn it on Overtype, just tap the key again to turn it off.