A developer should use a constant when the value may need to be reused, maintained, or changed across multiple parts of an Appian application.

Constants help avoid hardcoding values directly inside expressions, interfaces, process models, or rules. For example, values such as group IDs, decision thresholds, status values, document folder references, or environment-specific settings are better stored in constants.

This makes the application easier to maintain because the developer can update the value in one place instead of searching through multiple objects. Constants also improve readability, reduce errors, and support better application design.

Hardcoding may work for quick testing, but it is not a good practice for values that are important to the application logic or may change later.

Correct answer: Use a constant when a value needs to be reused, maintained centrally, or changed without editing multiple application objects.