"CAT improves the travel document checker's ability to accurately authenticate passenger identification and pre-screening status, addressing the vulnerabilities associated with ID and boarding pass fraud," the TSA website states.
A TSA officer can scan a traveler's photo ID at airports with CAT units. Then the CAT unit will link the traveler's identity with their flight details, including verifying that the traveler has a ticket for that day. This means you'll be able to get through security without having to also show your boarding pass.
According to CNTraveler, 176 airports are equipped with 1,621 CAT units. The TSA has a list of 119 airports where CAT units are currently installed. The new units will be able to scan US Passports, US Passport Cards, and multiple other forms of official documents.
You'll still need to check in with your airline and have your boarding pass to get onto the plane, but the removal of this extra step will hopefully make getting through security a bit faster. So, you'll have your boarding pass heading into the security checkpoint—you just may not need to show it until you get to your gate.