I learned a good lesson recently about why not to allow Facebook to be my only way to access to any website. I sent a request to one site and let them know I couldn’t access my account as I had only used Facebook to access it. The site was quick to respond and unlink Facebook from my account. Other sites may not respond as timely if you need to access a site that you never signed up for with an account, but only used Facebook or another third-party site to access. I am scheduling this mid-afternoon of Wednesday, March 13, 2019 and Facebook is still down when I scheduled it. It finally came back up later that night along with the other sites Facebook controls about 10 P. M. U. S. Central Time.
The above applies to other sites where you may use a different site to sign up, not just Facebook.
There are only a handful of sites where I use Facebook as my only log-in. I will be checking with those sites as to how I can unlink Facebook without losing my access. I don’t mind using Facebook to access some sites, but I want the ability to access the site without Facebook.