Acoustic Guitar Construction

On another forum I encounter a person setting up his shop in Arizona and he was going to a lot of trouble to humidify the shop to 40 percent rh. What's served? If the instruments he's making are staying in the Southwest, and humidity when he builds is normal for the region, and the wood has been allowed to acclimate to the dry air, what's the harm? I understand that for myself, in Connecticut, I need to be careful not to build when the humidity is elevated lest the guitars shrink and become concave in the winter without humidification...

Thanks for comments/observations.