Access request approvers may have a better understanding of what access the person should have and thus may need to modify the request. They may need to approve some of the requested access, deny other requested access and then add additional access.
This could especially be true when requests are done at the permission level. It may be necessary for a request for one permission to include a request for another. A similar use case could be the situation where a person requests access to a permission within an application, but they also need a request for an account in that application. In this case, the approver may add the request for the account to a request for the permission.