As part of its ongoing effort to provide more data transparency, Facebook is rolling out a new version of it's 'Why Am I Seeing This?' ad information panel, which will include additional insight on how each advertiser has chosen to target you, and the means they've used to obtain their targeting information.

As explained by TechCrunch:
"Starting February 28th, Facebook’s “Why am I seeing this?” button in the drop-down menu of feed posts will reveal more than the brand who paid for the ad, some biographical details they targeted, and if they’d uploaded your contact info. Facebook will start to show when your contact info was uploaded, if it was by the brand or one of their agency/developer partners, and when access was shared between partners."
The new information panel is the latest in Facebook's efforts to help users understand how their data is utilized - almost a year ago, in the wake of the Cambridge Analytica scandal, Facebook added new measures which put additional requirement on advertisers to confirm that any audience data they uploaded into Facebook's system was obtained through legitimate means. This new overview provides more transparency on this - now, if you see that your information was accessed from a questionable provider, you can raise a concern with Facebook and potentially see action taken against the company.
For marketers, this adds more accountability to the process, and puts more onus on them to ensure the data they utilize is legitimate. For users, it provides another way to understand how and why they're being targeted with each ad.
The new measures, as noted, will come into effect at the end of the month.