Row Level Security and members without roles

I'm getting up to speed with Power BI and having discussions with the business i work for its clear that there will be a need at some point to publish reports on places like SharePoint and want to use Row Level Security to mitigate risk.  So in a scenario where i can't know ahead of time all of the users accessing the report, what will users see if they are not a member of PowerBI security role?  (I understand that Pro licenses are required for this scenario, which isn't a problem).

I've tried searching for answer and couldn't find this particular question asked.  I'm hoping the answer is that they will see zero data, but my concern is that Power BI might return all data instead.  Any help would be much appreciated.