THE MORE YOU KNOW.
Advertising metadata is more malicious then anything FISA does. You can narrow down individualso based on time and place since ad data is geotagged. Correlate that with an advetising profile and your unique identifier that is 'anonymously for ads, becomes a hard metadata to be tracked across all platforms and apps.
Timmy loves John Deer and whole milk. Ad ID 1234 is an 'anonymous' ID for someone that likes these things. Ad ID 1234 is seen at Timmy's home and the mechanic shop he works. Oh, and at the gym. Sometimes it's seen with the Ad ID that likes flowers and cats, because Timmy takes his mom to the store every Saturday.