Matt,
What Glenn is talking about with knockouts could not be produced by turning off a Layer. Making the Layer Non-Printing yes, but not turning it off.
Example: You have a square background which is going to Foil emboss. On top of the square foil is a photo inside of a circle. The foil will be square with a circle area knocked out of the center. Turning off the layer with the circle will make it so the circle is NOT knocked out of the foil.
What Glenn is talking about with knockouts could not be produced by turning off a Layer. Making the Layer Non-Printing yes, but not turning it off.
Example: You have a square background which is going to Foil emboss. On top of the square foil is a photo inside of a circle. The foil will be square with a circle area knocked out of the center. Turning off the layer with the circle will make it so the circle is NOT knocked out of the foil.