I'd prefer they not. Nest uses fairly simple principles to make your house comfortable for you, such as working harder to maintain your ideal temperature when you're at home and by predicting when that's likely to be based on past experience.

Plotting the difference between inside and outside temperature versus time and looking for the intervals where they're closest together (that is, when Nest isn't working hard to make you comfortable) probably correlates very strongly with whether you're home at those times.

You might be comfortable with Google being able to predict when you'll be home. I can imagine a lot of people who wouldn't like that at all.