At the same time, the people who use this data also has to recognize its limitations.
When considered collectively, it is probably fine for an overall picture but it will have some limitations. For example: the people who are not submitting data (whether they found some way to disable it or simply don't use the technology) probably live a sufficiently different lifestyle to render the generalizations meaningless for that population.
When considered individually, it can be disconcerting. The accuracy of location data can be an issue. In urban areas, being off by a few meters can associate a person with one population instead of another. Data classification is another reason. In my area, it is currently a summary offense to enter a park. That can create problems for parks workers. The issue may easily be resolved, but it creates headaches at a time when people have other concerns on their mind. Then there is abnormal device usage. Exactly how do you treat people who leave their phone at home 24/7 because they have no use for it (currently unemployed), do not want to be tracked, or are simply unable to leave their home?
It is easy to argue that these people are professionals who know how to handle data, so limitations will be recognized. That's certainly partially true: governments, police, health officials, and the fine folks at Google are professionals who know how to handle data. The thing is, they typically know how to handle their own data and may not be familiar with handling data from other sources.