True, but it wouldn't hurt to hold for ON TIME pax coming off of SCHEDULED connections.
UA schedules connections that they KNOW will be impossible to make. You and I know they'll be impossible to make, but Granny and Granddad don't know that you can't get from IAH terminal B to T-E in 45 minutes.

And that's 45 minutes to from arrival time to departure time. So, deduct time to get off the plane, figure out how to get to the other terminal, and get to the gate before they close the door. In reality, you might have 15 minutes of actual transit time if you don't stop at a bathroom.

(Another war story.) My wife and I flew DL IAH-SLC-COS once. We departed IAH late. Ran to the plane at SLC to find the door closed. They wouldn't open it. We had SIX hours to wait for the next flight. Our scheduled plane had two hours on the ground in COS before returning to SLC. It would have cost them nothing to take a couple extra minutes to board us. Different airline but UA is infamous for this.

I fly UA all the time because IAH is my nearest airport and I can fly pretty much anywhere I want to go non-stop, thus avoiding connecting flights for the most part.