In P6 Analytics there are some excellent reporting abilities for Roles I would like to focus on. The ability in P6 Analytics to slice and dice data by different areas allows you to combine information related to Roles and view it in an Analysis.For example, you are staffing multiple projects, you do not know the specific resource that will work on this task so a Role is assigned at the time. Later on as you staff those Role assignments you will need to see across your enterprise how your Role assignments look and which ones still require staffing.
Here is a screenshot of a very simple analysis which can show this.

With P6 Analytics you can also add in other areas to help further slice your Analysis, such as Project.
If you are interested in seeing a static Resource Limit that goes along with the Resource assigned to the Role you can accomplish this by adding a new join into your RPD.
In the Physical Layer of the RPD you will add a join between the w_resource_role_d and w_resource_limit_f. This will allow you to join the Primavera Resource Assignment and Primavera Resource Utilization subject areas and add Resource Limit into this current Analysis. This is just a static Resource Limit, not related to Role or a Role limit.
Here is a screenshot of the join in the RPD.

After making the change in the RPD the OBI services must be restarted.
There is more that can be accomplished with the Resource Assignment subject area around Role and Resource usage and staffing. By using this subject area you can see enterprise wide role and resource usage, or filter down by assignments.