You should create a bespoke issuer if you want to use your own dedicated source of identity. If you manage users in a google workspace, azure Active Directory or any other Identity provider which supports OpenID Connect (oidc) this is a reasonable choice. If you need access to settings from your own Identity provider. For example, if you want all users on this identity provider to be provisioned automatically, or if you want to use multi-factor authentication from your identity provider itself.
See https://www.agilicus.com/anyx-guide/authentication-issuer/ for more information.