For internal US flights Pre Check is a god send! That said, I'm on a domestic AA flight out of LAX right now and lone behold the Pre check at terminal 4 was closed. So, I had to pull all my liquids out, take my laptop out etc and there was general chaos from the folks who are used to Pre and leaving everything in their bags being made to drag out liquids and laptops etc.

Usually I'm in and out of security in minutes with Pre (except tonight). Glad to hear our UK bothers and sister can take advantage of this service!