Posted By:
peter chaoI discussed this on the flipping thread. It's the two shoebox approach to collecting. In the first shoebox are all the cards you want to keep and in the second shoebox are cards you are willing to trade or sell.
The idea is to keep adding to your first shoebox. Don't sell any cards in the first shoebox unless you have to, that way you don't have to repurchase it in the future.
However, if you get tired of any cards in your first shoebox feel free to move the card to the second shoebox. 
Peter