It's right there in their privacy policy:
https://www.facebook.com/polic...
We collect the content and other information you provide when you use our Services, including when you sign up for an account, create or share, and message or communicate with others. This can include information in or about the content you provide, such as the location of a photo or the date a file was created. We also collect information about how you use our Services, such as the types of content you view or engage with or the frequency and duration of your activities.
and...
We also collect content and information that other people provide when they use our Services, including information about you, such as when they share a photo of you, send a message to you, or upload, sync or import your contact information.
The list goes on and on. Most troubling is this is how they descrie their "anonymous" data:
For example, we may tell an advertiser how its ads performed, or how many people viewed their ads or installed an app after seeing an ad, or provide non-personally identifying demographic information (such as 25 year old female, in Madrid, who likes software engineering)...
It has already been proven that anonymized data can be unraveled and associated with an individual again. Facebook makes it even easier to unravel by providing the sex, age, likes and city of the victim. (Search /. for the multitude of stories on this). So don't feed me that pap on it being "anonymous".
Even given the policy, Facebook doesn't come right out and say EXACTLY what and with whom they are sharing information BEFORE THEY SHARE IT. It is intentionally nebulous.
Lastly, the default settings in the Privacy Center is to share as much as they can without triggering aggressive privacy concerns generating bad PR. Admittedly, that is the whole purpose of the site. So the idea to not use social media or at most provide as little private information as possible (or fake it when not avoidable) is sound advice.