Collecting this information allows the NSA to quickly and efficiently identify terrorist cells. Once a single terrorist is identified, the NSA can query their database to identify the phone numbers in contact with that particular terrorist.
This ability to “connect the dots” was developed in direct response to the 911 attacks.
The best and brightest minds in the country developed this program & scrapping it now will undoubtedly make the U.S., its allies and interests abroad more vulnerable to attack.
The program is already vastly compromised by the Snowden leaks – scrapping it entirely will effectively blindfold the NSA.