Like subtypes, contingent values allow for abstraction at the domain level; however, contingent values take this abstraction much further by restricting the options available within the picklist.
Envision a scenario where you have a feature class of city streets categorized using three subtypes for local, collector, and arterial streets. The subtype is valuable to provide one level of abstraction and define different default values for speed limit (such as 25 miles per hour for local streets); however, there is nothing that would prevent an editor from choosing a value other than the default (perhaps setting this to 70 miles per hour). While other values may be technically allowed within the domain, they would be invalid in actual usage for this road type. Applying contingent values in this scenario improves upon the logic to constrain the options available for the subtype’s speed limit and prevent edits such as this from occurring. Additionally, validation is present during data entry to alert the editor to the presence of invalid values, which highlights impacted fields and disables the option to save.