Here is a video I made to demonstrate the difference between a static roll cast, a wiggle roll cast (WRC) and a switch cast. The switch cast is considered by many to be the foundation of all Spey cast. Roll cast is obviously necessary as well since all spey caster will need to roll out their line (taking out all the slack) in preparation for the actual Spey cast. The wiggle roll cast (WRC) on the other hand is a relatively new cast I invented for still water spey application and it is an excellent cast for situation where you have limited back room for a proper switch cast and yet want to get better distance than the conventional roll cast.
In this video, all three cast are executed one after another in succession so that you can directly compare and gain appreciation of the difference between them. Note that the static roll cast has the smallest D-loop and the least energy in the D-loop. With the WRC, the D-loop did not get very much bigger but has a lot more energy in it. That energy helps load the rod for a better cast. Last of all, the switch cast has the biggest and most energized D-loop and therefore produce the most powerful cast.