This was a primary goal of Google Plus: empower cookie / fingerprint joining. Even if Plus were to fail they’d still be able to harvest gmail and youtube for everything else.
To me it didn't seem a co-incidence that Google Plus was canned once Apple implemented their enhanced privacy features in Safari.
Google can already track you website to website with Chrome (e.g. shared browser history, amongst other methods), but on Safari per-site tracking such as how the Like and +1 buttons worked was needed.
Google can already track you website to website with Chrome (e.g. shared browser history, amongst other methods), but on Safari per-site tracking such as how the Like and +1 buttons worked was needed.