With Row Level Security, Audience Members Can See Only Their Data
Row-level security is a term that means any user viewing data can only see their own data. The "row" referenced here means that each row in a database table has security applied. You can imagine a spreadsheet, where you or I would see different rows of information based on the permissions that we have.
Typically, you will have audience members from different customer companies. If Walmart and Target were both your customers, you would only want Walmart employees to see their data, and Target companies to see theirs. Row-level security lets you accomplish that, without having to build a unique dashboard for every customer company.