As discussed in the standard instructions, when trolling your Tomic Plug, it is very important to place the knot as far up and centered on tow bar as possible. The elastic band method effectively moves the knot even higher up (and back) and therefore produces more action.
This will be especially important when fishing at slower speeds.
Note that 3/8 or 1/2 inch surgical tubing, cut thin, makes an excellent elastic band for this application.
This method is great if you are using different types of tackle at the same time, which need to be trolled at slower speeds. Plugs are normally fished above 2 knots, and this method will keep your plugs working at slower speeds. This method also seems to be good to use in areas where there is a lot of bait.
The Bead chain method is a variation of the same idea, which allows for adjustment of the towing position. Put an elastic band on the plug, to the tail side of the tow bar. Add a bead chain on your leader before the lure. Put the bead chain under the elastic band. You can now vary how much to pull the leader back by which beads the elastic band fits into. The farther back the leader is pulled, the more action the plug will have. Make sure that the leader is centered.