Hi @Sam P
For any process or request type where a customer is required, I'd start by making sure that there is a Wait for Customer node near the beginning of the workflow. If the customer is provided, the workflow will automatically move past this node and continue. If the customer wasn't provided, you can make sure that the person that copied the request also is forced to add the customer once the request is raised. Putting the Copy feature aside, if there are any dependencies in the workflow that requires there to be a customer such as sending an email to the customer it is always worthwhile having these types of checks.
Not all request types use the customer option and for those that do, the customer is optional within the request form. The only place where the adding of a customer can be made mandatory is within the Intelligent Capture workflow. Different customers and the services that they provide may all want to work with this differently so a blanket option to make the customer mandatory on the copy request from will be problematic for some. The workflow is really the place where you can make sure the requests have the appropriate information that you need while providing the flexibility for other services or departments to work differently.
I hope that helps.