One danger is that with all that data about you and very advanced AI/ML tech Google can push you into making irrational purchase decisions (yeah, I know YOU are special, and advertising doesn't work on YOU) - e.g. buying a red sports car in your 40s.
The other is this data will be available to NSA, GCHQ, etc. and their controlling governments, politicians, their wealthy sponsors/muppetmasters, etc. Do you trust the politicians in USA, or any other courtry?
We are all man and not angels. Having all data on someone, you can always find shady stuff. Using that government and big business can make sure there are no influential union leaders, political parties offering real change, etc. It will be the end of (however imperfect) democracy.