User blog comment:Kplate/Deck building and side decks/@comment-1755882-20141006025152

The idea can definitely work, but its very dangerous, as it has great potential to screw up your Game 1. I'm not talking about having a trash card for the match-up in Game 1, I'm talking about it really screwing with your deck's overall consistency. This ruins the charge & draw fix, as with more cards in your main, that fix to your dead cards is less likely to give you something you need.

The idea also loses a lot of viability going into the BT04 format due to how it won't be one dominant deck, as Goldritter, Legend, and Darkness Dragon are all up there with Dungeon in power, so you can't have a sideboard for a single dominant match-up in your main.

Another issue is that your Sideboard shouldn't be fixing an auto-loss. If your deck is losing so badly to the dominant deck of the meta, that's kinda a hint that maybe the deck is not a good choice for the format.