[lurker456]

Yes, to offer that functionality it would need a cookie. No, the website doesn't need to correlate that login and all activity related to it to everything else you ever did on the internet to build up a profile about you. It is technically feasible (even easier) to offer the first ("remember me on this one site") without doing the second ("track me across all sites").

[JetSpiegel]

Well, technically it's all the same, it's a request to FB servers with an user id and token. Decoupling that relies entirely on Facebook's internal policy. Since they are a public company now, not using that dsta is leaving money on the table.

[TeMPOraL]

Technically, at least for EU users, whether they do this or not should now be a switch on the GDPR panel.

[rock_hard]

Not using that data also makes the ads expierence for people significantly worse.

And I prefer seeing good ads over bad ones