You can add a list of External reps whose names will appear in the "Rep Name:" dropdown when creating an order, and also as an option for the default rep when editing or adding a customer. These reps do not need to have login access to Blastramp but can still be reported on for their sales and assigned to customers.
It is for reps that you don't want to login to Blastramp but still want to be able to report on their sales and assign the rep to a customer.
User Reps, on the other hand, are those with Blastramp logins who have different roles and access to various functions within the platform. User Reps only have visibility to orders and customers for accounts to which they've been assigned access.