Unless you are planning criminal activity in the future, this feature could act as an alibi to absolve you of being in the place where a crime was committed. And, false positives aside, I think it's great that law enforcement has the tools to keep society safe and civil. Law enforcement is not always == bad
Tracking the movements of all citizens is not a compromise that ought to be made to keep society safe. This power can and will be abused to target minority groups (closeted LGBT, minority ethnic groups..). Also in America law enforcement has too many times to count abused their power, and fabricated results from "evidence".
As any lawyer would say: Don't speak to the police, even if you're innocent. Same with this. If I personally want to share my own private tracking data that my lawyer says I can share.. sure. But I do not want this entire data free for law enforcement to see.
It's nice in theory but can also be helped to convict you if you happen to be near the wrong place at the wrong time. Interesting related video by Law Professor and Police Officer https://www.youtube.com/watch?v=d-7o9xYp7eE
That really makes no sense given how easy it would be to fake. You'd have to also prove you had possession of the device at the time.
What I could see happening is the absence of the data becoming a factor for increased scrutiny. Because, of course, if you don't have anything to hide... why did you stop Google from tracking you?
