Personally I have a fair amount of cards, If you're talking a combined Yu-gi-oh and Pokemon..that's too many cards.
I'm not really a collector so I don't have a lot of cards.
I mainly trade and sell cards when they are worth money for Yu-gi-oh and just keep the same old decks to play.
When a set rotation happens in Pokemon you are kinda forced to up your game and get newer sets and usually I will just give most of the out rotated cards away to collectors or they just get dumped in recycle bin.
My current Pokemon Monster binder has a lot of core supporters/trainers and EXs so I doubt they will get "rotated out" anytime soon.