Advantages to architects and builders

Freshly cut wood contains considerable water, which amounts to from one-third to more than one-half of the total weight. The drying of wood before it is processed into lumber is called seasoning, and is done for a number of reasons. Seasoned wood is far more resistant to decay than fresh wood; it is much lighter and therefore less expensive to ship. Most importantly, wood changes in shape during drying, and this change in shape should be completed before the wood is sawed.

In general terms wood may be seasoned either by air-drying or kiln-drying. Air-drying takes several months, whereas kiln-drying takes a few days. In both cases, the wood must be carefully stacked to prevent warping, and the rate of drying must be carefully controlled.
If you use 100-year old reclaimed wood the process is already done.