In the project configuration, you can use both workflow and field rules to set limitations on fields. Furthermore field values from selection fields with shared value sets and text fields can be set automatically
when creating dependent items or creating defects from test executions. Lastly you can also set default values for all item fields via the project and user defaults.
If you use more than one of these, the following order should be considered:
Furthermore the following behavior has to be considered:
Workflow rules that are designed to restrict the value selection of a field cannot be undone using field rules. Restrictive workflow rules are therefore the stronger rules.
The following properties in the workflow in particular, cannot be overwritten by field rules:
Softer rules, for example "editable", can be restricted by field rules and set to "not editable". Enclosed is the complete list of field settings in the workflow that can be overwritten by field rules:
editable (=> not editable)
not required (=> required)
highlighted (=> not highlighted)
not highlighted (=> highlighted)
The visibility as well as the highlighting have no influence on whether a value can be set or not. It is a purely visual aid.
Field actions that set default values to selection fields are overwritten by the "taking over field values between items" functionality.
If the target field is disabled by the workflow or a field rule action, it will be ignored and not taken over from other items.
The Templates with project defaults or user defaults overwrite any fields that where taken over from another item. Furthermore user defaults always overwrite the project defaults, if they exist.