Lots of good info above. Other things to remember: Everything varies.
GE gives you Precheck. But Precheck does not always get you the Precheck line - TSA likes to "randomize" everything, so occasionally those with Precheck are denied its use, and you still have to go through the regular line (I've had this happen to me a couple times, even though Precheck is available at that airport and that airline and I had used it many, many times). No rhyme or reason, that's how they roll.
Exactly what you do and don't have to do may vary from place to place and day to day (shoes off or on, iPads out or in, Nudi-scope in color or black-and-white, exactly what constitutes a puffy jacket, etc.). They like randomness, so be ready for surprises.
With Precheck's wide (and growing) popularity, it may not actually save you any time. I've seen non-Precheck lines that were shorter than the Precheck line. Doesn't happen often, but worth paying attention to if you're tight on time - you don't HAVE to use the Precheck line if the "regular" line is shorter.
If you're flying Business class (or First class, lucky you), you may have an even shorter "Premium" line available as an option. It's nice to have choices (sir, would you prefer the Dom P or the Krug as your pre-departure beverage?)
Precheck ain't what it used to be. There are so many people using it now, the lines are often quite long. Of course, you can pay more to upgrade to "CLEAR" which is even more expensive and typically offers the shortest, quickest lines (at least for now). See a pattern here? I expect in another year or two, there will be a "Platinum Precheck" option that, for a small additional fee, gets you whisked through security in a private limo while getting a deep-tissue massage and a pedi. We'll see.
Overall, it's better to have GE and Precheck than not have it. Enjoy the benefits when you can.
That reminds me, I need to renew mine and find my GE card...