Row-Level Security controls the data that is visible in a given report. Row-Level Security enables you to have only one version of a given report, instead of creating multiple versions of the same report but for different users.
For example, let's say you have a report that contains financial information for each of your locations. But you don't want each location to be able to see another location's information. Row-level security enables you to have just one version of that report.
While it is possible to not use Row-Level Security, most users will set this to Yes. Having Row-Level Security set to Yes and not setting up any row-level restrictions has the same effect as setting this to No.
For more information on how to create row level security, see the Row Level Security section