When will fire the customized attribute?

If you configure a Script-based calculated value, the script will be executed in three cases:

When a work item is created, the script is executed
When a work item is saved, the script is executed to recalculate the value.
When an attribute which the current attribute depends on is changed, the value of the current attribute is recalculated. Depending on the presentations of the two attributes this may not work in all cases.\


I get the answer from https://jazz.net/wiki/bin/view/Main/AttributeCustomization#Dependent_Enumerations_4_0