To allow users to control information sharing with advertisers, and keep those advertiseRd from interacting with you, in theory.
Like with Trump and the whole Cambridge Analytics debacle.
Presently this tool is being used in Korea, Ireland and Spain.
https://www.hackread.com/off-facebook-activity-tool-data-collected-by-websites/
Instructions for usage, and what tools do as well as , total deletion of account if you so, desire are listed in all highlighted links in article.
Too much information to even attempt an easy answer in plain English.
Froze
And yes, after long days/nights, I'd still like to swing these hunks of glass , plastic and silicon against the nearest wall Come on retirement!