"Allow sub-sites to use these credentials" unchecked and not working

I input the FB credentials into the Multisite settings and did NOT check the "Allow sub-sites to use these credentials" box and I went to the single site / main site / site #1 and the FB credentials were already in there.

What's the point of inputting FB app ID and Secret Key to the Multisite settings if you don't check the "Allow sub-sites to use these credentials" box? Does it only apply to the main site / site 1 or something?

FYI: I currently only have 1 sub-site (i.e. the main site) and having the FB credentials auto-populate from Multisite settings is fine there, but I don't want other sub-sites to auto-populate, which is why I did NOT check that box).

Thank you.