I started by reading this well written guide and understand its logic, but there is no tool/page to see what a given user has multiple access to. Besides, when you tie a banner to an usergroup and you give a user another group, either the banners stack, or only the highest one set is displayed depending of the settings, and that's doesn't always returns what I'm trying to achieve.
But thank you all for your input. Now that I'm here, what happens when two banners have the same priority number set? They both show?