The seeAllData=true annotation is used to allow a test class to access all data in the org, instead of using test data that is created in the test class or by using test setup methods. This annotation should be used sparingly and only when absolutely necessary, as it can make the test class dependent on the data in the org and cause unexpected failures or unreliable results. The seeAllData=true annotation is required for some sObject types that do not support test data creation, such as Report, Dashboard, Document, and Attachment. Therefore, if the test class needs to access a Report sObject, it must use the seeAllData=true annotation. Reference: [Isolation of Test Data from Organization Data in Unit Tests], [Using the seeAllData Annotation]