Just because reporting is so easy in ServiceNow it doesn't mean you shouldn't try to make it even easier. I would encourage customers and especially vendors to consider possible uses for the new Fuji report sources feature to make reporting even easier for end users.
Report sources allow app creators or admins to create predefined table filters that can be selected by report builders instead of a table source.
Consider including a report source in your app whenever you expect certain conditions to be used frequently. Why make the admins or users define the same condition over and over when they can simply select a source you've already defined? Report sources can also be helpful when a table name or label may not be obvious enough for users to locate the table from the report builder. One case might be when you want to direct the user to a database view instead of the table they might expect to report on.