Data warehousing is a methodology and not a technology. The purpose for the data warehouse is to make the reporting analysts life easy. i.e the data warehouse is built to facilitate reporting and not for enabling transactions.

There are multiple data warehouse designs, a star schema, a data factory, a flat file, etc. and neither is wrong - and the style / design implemented is determined by the purpose of the data warehouse.

Data warehouses can lighten the load on transactional systems and make transactional systems faster by being a repository of all closed transactions.

Data warehouses are designed to enable faster reporting. The data is pre-cleaned, harmonized and ready for reporting.

For example, the organization is investigating sales and why they are low in Saudi Arabia/middle east? With a data warehouse, it is quickly discovered that Friday is actually a weekend and Sunday is a weekday. It may also be discovered, from the data that the company processes were not optimized for Saudi Arabia and hence the sale are low.