Hm, looks like Google is trying to cash in on COVID-19 now. I really can’t think of any use for these mobility reports for disease control. The one for my region (backup), just to pick an example, says that there has been a 72% mobility drop compared to baseline for transit stations. Ok, there are about 493 train stations alone in Hesse, scattered across 21.114,94 km². So, how exactly is it going to help with COVID-19 planing to know that all of them combined are now seeing 2⁄3 less of an unknown number of people in a 24 hour period?
Of course, the raw data could probably be visualized differently, more precisely - e.g. for (paying) business customers.
What Google does here is using COVID-19 as a pretense to justify applying location data for different purposes than it was originally collected for and pitching a highly questionable, shelved product. So, for whom is “mobility trends” actually intended? I’d say banks and venture capitalists. This is pretty much an investors tool, but it also has military applications.