The user account consolidation was pretty explicit. It might have been explained as necessary for UX consistency, but for Ads it was a huge way to whitewash otherwise verboten underwear-smelling.

G+ birthed the "create account / log in with Google" widget for non-Google websites, that could go alongside the "log in with FB" widget that was getting popular. Those widgets let Google / FB join your account cookies with whatever other ads get shown on the page.

G+ lead to a dramatically changed privacy policy that dramatically increaed data sharing.