Shadow profiles: what do they contain?

I know this might be a trivial question, but what does a shadow profile usually contain? (those profiles that are usually created by Google, Facebook and etc. with identifiers such as sim number, IMEI, MAC address, ip address and all the others; I have even heard that the app list could also be an identifier)

I ask this because it seems that it is impossible to escape from Google and other companies even by trying to limit their services to …

address app companies escape etc facebook google ip address list mac mac address privacy profile profiles question services shadow sim