The Dashboard is a visual UI that is easier and sometimes quicker to use than the Management API. You can use the Management API from inside your application or from any other place such as a UNIX shell, a HTTP client or any other script or app. It gives you huge flexibility on how you want to manage your tenant and the data it contains.There are too many potential use cases for me to describe them all, from developing your own custom Auth0 Dashboard to provide users with administrative access or certain permissions (defined by the scopes that you can assign to the Access Tokens they could use).
As I mentioned in my previous response, there are several ways to implement roles and permissions. Currently, Authorization Core is not something that can be managed with a restricted SPA Access Token. If you take a look at Assign Roles to Users via Management API, you will notice that the Management API Access Token requires the scopes read:roles and update:users. We don’t have those scopesin a restricted SPA Management API Access Token as documented on Get Management API Access Tokens for Single-Page Applications.
If you really want to use Authorization Core and handle it via Management API, then you would need to call our Management API from your backend so you can have any scope you need without the restrictions that a SPA application imposes.