Users want to use custom fields as mandatory for Service Desk.
Now if you create a custom field you are not able to set it as mandatory, or even as a condition or validator on workflows. Customers open tickets missing information for the agents, so they need this field as mandatory to improve the Support for customers. At the moment you are able to set fields for Service Desk, although they will not be settled as mandatory.
There isn't any workaround besides asking it to the customer, loosing time on the process.