Last time we had a privacy officer make a report on our setup, we were (unknowingly) sending much more PI data to Google than the IP. The fact that you e.g. clicked the "like button" on profiles/xxx, leaks that you have access to xxx, can like it, and have liked it. There were many more like this. Ours was a business tool.

The data we were leaking was e.g. the fact Foo was employee at ACME, simply because we sent events occurring on the estate of Acme for user Foo.

It's not as straightforward as proxying. Or, as we did, removing some bits from the IP.