A normal user would have an operator record in the system to process work. A work party is a person, business, or organization associated with the case. A work party does not need to be associated with an operator record in the system. You could be adding a work party for a contact that will then receive email correspondence related to the case.

Hi,

In Pega, you create a work party to describe each role. As mentioned by Carissa, a work party is a person, business, or organization associated with the case Work parties allow you to refer to a case
participant by role, without knowing any identifying information. For this reason, applications
commonly use a work party as the recipient of correspondence. Also, work parties are sometimes
used to assign work.

In Pega, each user is represented by an operator record. The operator record contains information
such as the operator's name, position, organizational hierarchy, and location.
Each operator is a member of an access group. The access group record describes a set of privileges.
These privileges are available to users who belong to the access group. Any operator can belong to a
number of access groups. However, only one access group is active at any time. The access group also
indicates the portal through which the user interacts with Pega.

Regards,

Vikash