Porcello ultimately has to make the pitches, but IMO, having a catcher that you trust and have confidence in makes all the difference in the world. Some of it will show up in the numbers, but much of it doesn't.
Trusting what your catcher is calling for and not having to overthink, having confidence in throwing breaking balls and knowing your catcher will block the ones in the dirt, knowing that you don't have to be "perfect" in hitting your location and still get a strike, and not having to worry much about holding runners on first all have to have a fairly positive impact on the pitcher.