[hedora]

I only log into Facebook to tighten the privacy settings (I probably should just delete it, but they obviously had already built a large shadow profile for me before I created my account; presumably they’d keep doing that after I deleted it.)

They gather tons of my information from third parties, often through data sharing deals.

For instance, when I bought a car, the manufacturer somehow linked it to my Facebook account (without my knowledge or consent, and I don’t have a car app installed on my phone).

However, the vast majority of their profile on me is from cross-app sharing.

[manigandham]

If you do business and give data to a company, whether through an app or some offline interaction, then they know who you are and can sync that data with Facebook or other ad companies as long as it follows regulations.

This change only stops easy syncing of a profile based on a stable device-level identifier, often used in (semi-)anonymous situations (like app install ads). It doesn't mean companies can't share data ever again.