Although mildew, rust, and corrosion are the enemies of goods in storage, they cease being threats when the moisture is substantially
reduced in the storage area. Generally, an atmosphere of less than 40% RH keeps these degradative processes dormant.
Maintaining a dormant state is also important for seed storage. For example, if corn seeds are stored in ambient conditions, it's possible that as few as 7% will germinate the following season. Contrast that to seeds stored in a controlled environment; they usually germinate in the 90% range.