I find two things it does. First when displayed info about clips in PB mode you get access to meta data when you press exec. You can also use this button when choosing multiple clips in PB mode.
There is not a printed version of volume 2. Enjoy Barry's book and for me, I find answers way faster in the electronic form anyhow. I don't know where my paper copies of of virtually everything I have broght to the market since 2002. I do know exactly where the electronic ones are. ;-) Put it on your iPad, or droid.
The EXEC button is used for certain functions, and you'll know what they are because it will be displayed on the bottom of the LCD when there's something for the EXEC to do. Primarily, you use it when deleting clips -- the EXEC button executes the actual delete process. And, as editman says, it allows you to see the metadata when you're in the clip properties.