For example, it might be reasonable to extract sales data on a daily basis, however, daily extracts might not be suitable for financial data that requires a month-end reconciliation process. Similarly, it might be feasible to extract "customer" data from a database in Singapore at noon eastern standard time, but this would not be feasible for "customer" data in a Chicago database.
Data in the Data Warehouse can be either persistent (i.e. remains around for a long period) or transient (i.e. only remains around temporarily).
Not all business require a Data Warehouse Staging Area. For many businesses it is feasible to use ETL to copy data directly from operational databases into the Data Warehouse.