Difference between Ess Job Derived attributes and Attributes

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We are creating Custom ESS job for one custom report requirement. We need know, what is the real-time use case of Attribute and Derived Attribute from above screen, Column Selected in Attribute is going to send value as parameter to main query but we see + option in Derived Attributes section, where in if we add multiple attributes still ess gets the single attribute value passed to main query. What is the use of derived attributes here?

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