Suppose you employ a manager who will be responsible to handle all your business activities in a particular Zone, let's say, Chicago, you are able to assign him to that particular zone while creating his user from Admin Dashboard.
This ensures your manager can only access data and operations related to the Chicago Zone of your business.
You can assign delivery boys and even other custom user roles based on your area of operations to Zones. Like, Delivery Boy Jason lives in Chicago so he can be assigned to Chicago.
This allows the Zonal manager to manage all the activities like cash collection, payouts, commissions, etc. of the particular delivery guy, helping you in delegating your workload to your manager.