By resource - the resources accessed.
By group - the user groups assigned to users who were transferred to resources. Not available across organisations.
By permission set - the permission sets assigned to users who were transferred to resources. Not available across organisations. Permission sets are reported whether or not they contain the resource in question.
By location (coming soon) - the countries that the users were in when they were transferred to the resource.
By custom attribute - any custom attribute you have added to your schema and marked as reportable.
These breakdowns can be viewed for all resources or a single resource by selecting a resource from the dropdown at the top of the page or clicking on a resource name on the all resources view.
If you select resource as the breakdown, you will be presented with an option to select an additional breakdown - e.g. permission set, group or any reportable attribute. As this can make the interface a little crowded, downloading the report may be helpful.
Anything to watch out for?
The attributes used in some breakdowns can have more than one value for a user - the most common is permission sets, but you may have others. When breaking down by these attributes, the sum total for the attribute can be larger than the total transfers for the users because the same user action can (and should) be counted against each value. With permission sets, you need to know that the key connection is the user rather than the resource which means it is possible to have stats against a permission set for a resource that is not assigned to that set when users have other sets with the resource assigned to them.