If you wish to delete participants from the survey completely, it is best to remove these from the participant list. This will result in a change in the assessment matrix.
It is also possible to delete participants in the assessment matrix, however a participant will then only be deleted from this current assessment/questions. This only makes sense if for some reason the calculated evaluation matrix for a combination employee/colleague, colleague/colleague or superior/employee is not feasible or, for example, you would like to create a personnel file for the employee but this person has only started working for the company and therefore cannot meaningfully take part in the 360-degree feedback.
Then the status for this person is Participant is not an assessor.