Photon parallelizes hardware writes for servos and motors to make your robot's loop times faster. This is a stable version of the now-archived PhotonCore, that doesn't have probems.
Normally with the SDK, after a setPower() or other LynxCommand, it waits for it to finish and check that it happened. But with Photon, after a setPower() or other LynxCommand, it immediately moves onto the next line of code/hardware write.
It is most effective with Swerve, because of the high amount of hardware writes frequently happening (4 servos + 4 motors).