You really have to be careful to watch the pleater thread or it could get caught in your stitches and be harder to remove at the end. The other thing Ms. Brachey's video recommends that I disagree with is her instructions about stitching a row of cable stitches. She recommends placing the needle just above the pleating thread for a up cable and just below the gathering thread for a down cable. That is the reason that you see fabric showing between her pleats. The fabric gets caught when the row is stitched.
Fabric showing between the cable row is probably the biggest no-no in smocking.
If the pleater thread is used as a guide, I suggest that the gathering thread should be used whether the stitch is above or below the gathering row. When stacking, if the first stitch on the row being worked is an up cable and the stitch below is a down cable, I suggest placing a needle just above the down cable, facing to the left. This gives just the right space to be left when the up stitch is done on the row above. The up cable has no guide to use unless it is stitched on top of a gathering row. If a smocker is considering purchasing Ms. Brachey's video, you might want to consider seeing if you can rent or borrow it from your favorite needlework shop or sharing the cost with several friends and sharing the tape.