Sometimes the value of a property is reduced not because there is anything deficient in the building itself, but because of factors external to the property. Imagine owning the very last wagon wheel factory - the plant might be highly efficient and very well maintained, but the market has gone away. Today the rise of portable computing devices has negatively impacted several industries. Increased globalization has resulted in a geographic shift in manufacturing.  If an affected facility can't be easily re-purposed, then it likely should receive a reduction for external obsolescence. There are many other examples of how such external factors can reduce the value of a property - is your facility affected?