By using a data warehouse you are in effect providing a common data model for all data that is of interest without having to be concerned about the origin of the source. This ability makes it far easier to compile a report and analyze all available information than it would be if you had to retrieve information, invoices, ledgers, orders and so on from a multitude of data models.
Before the data is loaded into the database it has to be cleansed, in effect this involves identifying and resolving all the dirty/inconsistent data. By doing this before the data is loaded into the database the actions of reporting and analyzing data are greatly simplified.
Once it has been loaded into the data warehouse the information is under the control of the user. This allows for the information in the warehouse to be stored safely for extended periods of time, even if the source system data is purged over time,
Another great advantage of using a data warehouse is that they are separate from any operational systems. This means that they can perform retrieval of data operation without interfering with any operational requirement of the system.
Data warehouses is also able to work in conjunction with, and by doing so enhance the value of, operational business applications, the most notable of which being customer relationship management (CRM) systems.
Data warehouses are generally used to facilitate applications associated within the decision support system. These applications will deal with reports concerning trends, for example what was item had the best sales in what area over the last year, exception reports, and reports that show actual performance versus goals.
The ability of data warehousing to compile, analyze and report information from different sources to give valuable information quickly rather than trawl through information from different sources in different formats is priceless in this age of instant decision making.