I just recently attempted to set up Facebook adverts for an app I developed. When it came time for me to set the metric up I obviously chose "App Installs" as my metric to track.
To do this, Facebook told me I needed to install the Facebook SDK in my app to attribute an adverts conversion.
I didn't end up running the ad, but I can see why companies potentially have the SDK embedded in their apps to track ad-spend, hence the phoning-home to Facebook.
Edit: Just so people don’t have to dig to verify;
https://en-gb.facebook.com/business/help/2083260191704068?id...