A new study produced by the Privacy and Civil Liberties Oversight Board (PCLOB) found that the NSA's program analyzing call detail records yielded only a single significant investigation between 2015 and 2019.
Of the 15 reports citing call detail records, the PCLOB states that the FBI received unique information from only two. “Based on one report, F.B.I. vetted an individual, but, after vetting, determined that no further action was warranted,” the PCLOB states. The second report “provided unique information about a telephone number, previously known to U.S. authorities, which led to the opening of a foreign intelligence investigation.”
You can read the study here and below.