You can read the brief details here:
Please be advised, this is a direct UPDATE via SQL operation on the database.
You cannot just "undo" this - so be every careful !
You should definitely make a copy of the database first, and be sure that you know how to restore that database before you run this script.
I have used this function maybe a dozen times now ver the years, and it only ever failed once (and that was because the server in question already had several other major issues).
Hoe this helps, Stuart.