What does before-and-after rule mean?

before-and-after rule meaning in Law Dictionary

ppraising home value before and after a house is damaged or enhanced. This occurs when a property is condemned.

before-and-after rule meaning in Business Dictionary

The practice that is accompanied by many jurisdictions of appraising the property value both before in addition to following the taking, deciding on improvements or injuries on home that were the result of the condemnation.