Moreover there's value in seeing how that targeting applies to real people in practice.

It's great to be able to see what ads campaigns are running, but if you're a real user, who's feed is full of ads from overtly partisan news sites, clothing companies selling aggressive political gear, AND all the campaigns and SuperPACs, what does your experience look like as a whole?

Our information environment is festering. I can't speak to any given study or technique, but we need to understand this stuff.