Don't confuse UI Policy Scripts with Client Scripts. They are not the same thing.

"UI Policy scripts use the client-side API to execute script logic based on whether the UI Policy condition tests true or false. Use UI Policy scripts to create complex conditional checks or to take actions other than setting field attributes (mandatory, read-only, or visible).

The scripting fields for UI Policies are only visible in the Advanced view. To enable the scripting fields, select the Run scripts option.

• The Execute if true script executes when the UI Policy condition tests true.
• The Execute if false script executes when the UI Policy condition tests false."

https://developer.servicenow.com/dev.do#!/learn/learning-plans/quebec/new_to_servicenow/app_store_le...