Normally, each time you run an interactive plugin, the dialog comes up with settings initialized to the values you used the last time you ran it. Sometimes this can be very annoying, if you mess up the values and don't remember what they were originally. One way to recover is to exit from GIMP and start again, but this command provides a slightly less desperate solution: it resets the values for all plugins to their defaults. Because it is a dramatic step, it asks you to confirm that you really want to do it. Be careful: this command is not undoable.