The main reason why an ODS or Operational Data Store is often build is to give users the possibility to execute operational reports. An ODS can be seen as a (partial) copy of the source system. It typically is also then the source for ETL related activities. The granularity is the same as the source system.
Most technical data integration solutions have good synchronization methods to sync the ODS with the operational systems. The only issue that can appear is the availability of the data in time or in historical context when directly reporting from the ODS. Managerial reports typically require a higher level grouping, the combination of sources and/or the aggregation of data. This is the reason why an ODS is not perfect for analytical reporting and data warehouses are being build.