I can't really answer for Ed and I don't remember exactly what point he was making in that presentation, but I would not drive the surfaces/solids directly from the master sketch. I would make another sketch and convert entities from the master sketch. That way the master sketch is not consumed in the feature.It sits at the top of the feature tree and is always visible and available. By converting entities you maintain the link to the master sketch, so that it truly is the "master".
If you have just been viewing the slide show, you might want to look at the notes for each slide. Ed often includes really thorough notes that explain the reasons for doing things the way that he does them.
A layout sketch is exactly that, a layout. It is the skeleton for your design.
That said, it is important that the layout sketch remain accessible at the top level of your design. It should not be used directly to create any features which migh subsume it.
To use elements of the layout sketch for making features, one simply creates new sketches and uses relations such as Convert Entities or Offset to relate feature sketches to the layout sketch.
You can also use the layout sketch to create reference geometry (planes, axes, etc.), and even for mates.
I use layout sketches at the top level of a layout assembly. When a part needs to use the top-level layout sketch, the relevant parts of the assembly's layout sketch are copied into the layout sketch of the part. This greatly reduced the number of potentially troubleson in-context references, and creates a central point from which in-context relations are managed.