Defining personas (particular user profiles of people who will use a product) is considered essential for ost wen apps these days. But you can also make use of personas in an ERP project.
First of all, do not mix up personas with the system roles that are often used to define permissions sets and functional role centers in current ERP systems. A persona is more of an abstract concept than the concrete definition of a system role and its linked permission set.
A persona may be linked to a use case in that each persona demand a specific uses case to satisfy their needs.
So if you have a persona - order entry clerk - then the persona definition should make clear what a day in the life of this persona is like in order to define and to justify the functionality needed to populate a use case for that persona.