We allow the wood to equalize to reduce any wet spots that some people experience with other kiln dried slabs. Stabilizes the wood: which greatly reduces wood movement over regular air dried wood. It doesn't have the same moisture content swings that are seen in air dried lumber as well. With softwoods, it sets the pitch/sap. By setting the pitch you prevent it from oozing out sap during hot months.
This is a common occurrence when the wood hasn't been kill dried properly. It equalizes the wood and acclimates to a moisture content of an interior condition environment. It sterilizes and eliminates nasty little critters and bacteria.
No one wants a surprise after bringing a piece of wood into your home.