Most likely biometric data on crime suspects to correlate with other forensic data. Obtaining this data on a case by case basis is expensive so it is most likely to be used in high stakes cases like murders or bank robberies where police and prosecutors need to show a win.

For example, A is known to have been an associate of B. B died violently at a certain time and date. Phone data put both of them in the same general area around that time. A seems evasive and won't talk. But A's biometric data reveals intense physical activity around the time of B's death...

Other suggestions in this thread like algorithmically making things worse for people in general are predicated on continual availability for a whole deanonymized population.