Data researcher and artist Mimi Onuoha looked at the personal location and messaging data from four groups of people in a project called Pathways. It's less about how much we can find out from a person's traces and more about what the data doesn't capture.
The interesting thing about this group was the degree to which their data couldn't capture the reality of what they were experiencing. I was present for the goodbye their data leads up to, and I witnessed every bit of its difficulty. But data visualizations add a level of abstraction over real world events; they gather the messiness of human life and render it in objective simplicity. In life, goodbyes can be heartbreaking affairs, painful for all involved.
But on a map, a goodbye is as simple as one dot moving out of view.