Lies, i use it to train so that i can read my opponents attacks very well. the more you use it the more diligent you become. so please only use it until you have to go into tourneys. Think of the hyperbolic time chamber from dbz.
That's fine to believe, but like shadydentist said, percision isn't accurate. Moves end up becoming different when playing on regular speed at a tournament. IMO. The transition from lightning to regular would be too great.
Take Fox for example. His WD is pretty much instant, as you have to press X/Y and L/R with little time in between. So when on lightning mode, it's impossible. Or at least it is very hard. Or taking someone like Luigi whose WD has a slight pause in between the buttons. When in lightning mode, the pause is way less. When going back to regular, WDing with Luigi would be much different.
This is a little more situational. But if it's to enhance your reflexes, that doesn't really work either. Let's say you're a Fox against a Marth. The Marth runs to grab, but you dodge. The playing on lightning mode causes you to dodge as soon as you see the Marth dash. It happens too soon, and the Marth can punish you.
If you want to build your reaction time, than just play on regular mode. That way when you have to play someone else, you don't have to convert your playing speed.