btw, clearing your decks is pointless, unless you are creating a new deck (say, you have a beatdown deck but now want an exodia deck and a discard deck, and you want to be able to easily switch between them). El Bastardo said that he cleared all three decks and used the best 40 cards from the three, but this doesn't make sense.
here's what i mean: let's say you started with no blue-eyes white dragons. you just opened a booster pack in the game and got one. now, you can put it into all three of your decks at the same time, even though you only have one actual card.
if you had real cards, think of it as having all your cards in a binder, then constructing your deck from those cards. you then write down what cards are in that deck. when you switch decks, you pull apart your old deck, put the cards back in your binder, and make a new one from your binder. you write down what cards are in this deck too. when you switch back to the old deck, you pull apart the new deck and reconstruct the old deck from the list you made.
the three deck system simply automates that process for you, so you can have three 'card lists' that you can easily switch between. so, you aren't "freeing up" cards for use in other decks if you clear a deck.