One of my friends had an interesting remark about the "privacy opt outs". It's that google always tracks you, no matter what checkbox you check or uncheck. Why not use the data they are already collecting about you to improve your daily life then.
However, I don't use a VPN or spoof my User Agent. Google 100% knows who I am without using any fancy tricks. I've wondered -- wouldn't I be better off logging in everywhere, with my Google privacy settings flipped to maximum? While it's certainly possible for them to map my fingerprint back to my account(s) and opt-out preferences, I think that's a bit much to expect for them. I might be shooting myself in the foot by always being logged out!