What are “Sideboards” used for in Magic tournaments?

Sideboards in Magic tournaments serve the purpose of allowing players to modify their main deck between games, making option B the correct choice. In a typical match, players can consult their sideboards after the first game concludes. They may swap cards in and out of their main deck to better tailor their strategy against their opponent's deck. This flexibility can be crucial in adapting to different matchups and enhancing chances of winning subsequent games.

The sideboard typically consists of up to 15 cards that players set aside from their main deck ahead of time and can access only between games, ensuring a strategic edge without altering their primary deck entirely. The concept promotes dynamic gameplay and tactical adjustments, which is an essential aspect of competitive play.

The other choices focus on aspects like deck construction, score tracking, and storage, which do not accurately capture the specific function of a sideboard in tournament settings.