It might happen that when you are unit testing reports or data models you will probably encounter various issues. Tracing back the data is one of the steps you can execute to find the cause of an issue. In order to trace back the data you will have to know from which source it is coming from, at least when a data object is loaded from multiple sources.
By selecting the request ID as a characteristic you will be able to see which specific data load is responsible for a record. With the use of the SAP BW transaction RSRQ along with the request ID, you will be able to go straight to the monitor of the data load and determine that source of a record. Hopefully this information will help you in your journey of solving SAP BW data issues!