Extended properties are used to allow the business organization to store business specific properties. These properties can be configured by job types. You can configure one-to-one or one-to-many relationships. The following doc can help you understand how to configure the extended properties in Workflow Manager Desktop Administrator.
The extended property values populated from the Workflow Manager jobs can be referenced by token to be used as input throughout your workflow. The following doc is talking about using tokens as dynamic properties while running the workflow. The token can not only be referenced to extended properties but also job properties, etc.
Feel free to let me know if you have use cases in mind and would like to consider using extended properties. I will be more than happy to discuss it with you.
Thank you for the response. My use case is Right now we are assigning job to a group but we are not able to display users list so that higher authority can select a respective user for a job. For this user case how I can use extend properties.