Earlier quoted context omitted.
What's the point of signing in at all for users who don't use sync?
(if my understanding is correct) Consider the case of two users, Alice and Bob. Alice has sync enabled, Bob does not. Bob wants to check his email on Alice's computer, so he logs Alice off and logs into to his account. This syncs across all website he visits (due to shared auth cookies), but doesn't sync to the browser itself. Chrome is still logged into Alice's account, so Bob's browsing history is synced, but to Al…
To me that seems like a decrease in privacy.