Many IDEs will check for changes to their opened files made by other programs. This is usually done with a quick check when the IDE's window gets focus.

A dialog will tell the user the file has changed on disk and ask if they want to reload it. This dialog is only shown when the file has changed AND there are unsaved changes made in the editor. Otherwise, the file changes are just silently reloaded. (This is the behavior of Sublime Text.)

Notepad++ always asks, even when the edit buffer is not dirty. Actual use case: edit file with tkinter import and run in 3.4.  Works.  Open file in 2.7, changet tkinter to Tkinter, and run it.  If I click on the 3.4 wndow, I do not want it silently changed.

Here is my expert use (with changed edit buffers).  Hg nearly always screws up merges of Idle entries in misc/NEWS (skip the whys).  So I open the two or three required versions in Notepad++, edit all to how they should be, save the earliest (currently 3.4), go to TortoiseHg, commit, and merge forward (currently to 3.5).  If there is a conflict, revert to local, activate the 3.5 Notepad++ window, click NO, save, go back to TortoiseHg, mark resolved, and commit.

I am curious when beginners would need this feature.