Explanation
Excluded Resources are used to prevent certain service resources from being assigned to specific accounts or locations based on customer feedback or preferences. Assigning the Technician to a new Service Territory would affect all their service appointments, not just those for that Customer. Removing the Technician as a Preferred Resource would not prevent them from being assigned to that Customer, but would lower their priority. Creating a new Work Order Validation Rule would not affect the scheduling or optimization of service appointments, but would only validate data entry on work orders. References:
https://help.salesforce.com/s/articleView?id=sf.fs_excluded_resources.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.fs_territories.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.fs_preferred_resources.htm&type=5