I've misclicked on this many times while trying to save.
The literal interpretation of the function name sounds like that it will undo any changes I've made to the code after the last save, and google tells me that apparently, it's supposed to give me a popup window to confirm what I just clicked was intentional. But I have never received such a warning. I couldn't detect any changes made to the code either. It almost looks like it did nothing at all.
So I don't know what it does. What does it do actually? And is it safe to have it placed right under the save button? ("safe", as in, won't cause any issues in case of misclicks)