Need help understanding groups.

Need help understanding groups.

I am not sure how groups is supposed to be used. I am trying to set up requestors in a group, and another requestor as the approver of that group. I create a requestor group and add requestors to it. I create role names in organizational roles under groups, however the only groups I can assign to these roles are technician groups. So I'm not sure I understand the point of requestor groups. 

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