And they don't put you through the nudie scanner (or whatever it's called) which is important to some people. I have pre-check automatically through global entry (that basically lets you bypass immigration coming back into the US).
Just got ETA for the UK and you also have e-entry (which usually works) from the US and a number of other countries as well.
Usually true, though I don't believe that's guaranteed.
And all the lines at IAD have the new, high-powered luggage scanners (for carry-on, so still less powerful than the ones used for checked bags). So for those of that fly with film camera gear, we need a hand check with or without pre-check.
Just got ETA for the UK and you also have e-entry (which usually works) from the US and a number of other countries as well.