So, exactly like a knife? Generally we don't want to cut people open, but when we need to do it, like during surgery, a sharp knife sure helps.

Agreed mostly. The intent is local cleanup before you push like fixing a wrong author email across a batch or dates from a machine with a bad clock

Based on the name I have to imagine the author knew this. A knife is a dangerous tool if used improperly, and invaluably useful when used properly.