When using Android Auto , the big search machine will have access to the OBD data of your car and can judge if you are over-speeding, can judge the style of your driving, etc...
They will know how deep you pressed the pedal, what charge you have in the battery, if you overstress maintenance periods or not, ...
They will know what advertisments they could show you as they know your home and your place of work, etc...
Such data is also potentially interesting for insurance companies, authorities, etc...
Speedy drivers could face higher insurance tariffs, actual metering of speed data could lead to judgement of "gross negligence", etc...
It's up to you if you trust the external companies sufficiently for sharing such data for the comfort of having an actual navigation system.