You didn't miss anything. I haven't had a chance to update the workflow description on my site. There is a brief description in the MEL header and associated readme file, but, to make things easy, I'll do a quick description here.
"Initialize Mesh" does a couple of things. First, it deletes the selected object's history. As we all know, construction histories have been known to cause a few hiccups here and there. Second, it applies a base material to the object. This base material (materialID000) is used for a couple of reasons. The material's color 0,0,0 so it is easier to see unassigned faces when you're applying materials. It's also a way for me to make sure that no other fancy material or shader is applied to the mesh that might screw up the layout process later.
"Check Mesh" evaluates the selected object to see if all faces have materialID's assigned to them. It basically checks to see if materialID000 is still applied to any of the faces. If it detects it, all materialID000 faces are hilited in the modeling view, so you can easily track them down and assign materials to them. Once all faces have non-zero materialID's assigned, you'll get an all-clear message.
Basically, Initialize Mesh and Check Mesh are 2 additional functions to minimize the number of potential errors in the unwrapping process. They're not absolutely required, but I've found that they do help, especially if you work really fast and happen to miss a few faces here and there.
So, that's basically it. Let me know how the script runs for you.