If I can answer for Joe - the tape goes over the areas where the masks butt up against each other. I used them on a Spitfire, and if you think of the wing roundel (two colors), I painted the blue outline first, then laid down the mask and sprayed the center red. I then put down the mask over the center, but as they're vinyl, they can be tweaked a little, and the seal might not be perfect, so I put tape where the red mask met the blue one, and then sprayed the rest of the plane. The tape is just to prevent some of that other color falling between the joints on the masks, and you leave the outer edges alone.
-BD-