Because real wood is sensitive to moisture as it relates to dimensional stability. When wood absorbs moisture from the air it expands slightly. When the air around that wood becomes dryer the wood contracts slightly. Acclimating the plank flooring to the house gives the planks time to adjust to the moisture content of the home prior to install. This will minimize any change in dimension over time. That way you will minimize seems and or buckling in the finished floor.
The proper way to acclimate the planks is to sticker them inside the home for approximately two weeks. To sticker is to place small (1”) sticks between each plank as the planks are stacked. This allows air to flow to each plank. At Vonderosa Wide Plank Flooring we provide this service.