>>528248928
When you make a custom deck and press the "complete my deck" button the game at least attempts to assemble a coherent deck out of the cards you own based on blizzard's internal winrate data.

I have pretty close to a complete collection so when I pressed it gave me a deck that was 2 cards away from being a very competitive aggro priest deck, though the 2 cards it choose to cut were kind of questionable even then. Pictured here on the right.

On the left is "core priest' which is chock full of cards nobody has even attempted to put in their deck.