In the traditional approach to automation, each enterprise maintains its own resources (data centres, applications, servers, clients). This entails high fixed costs, for equipment and personnel which is typically not used to its full capacity (e.g., an application may be needed 10% of the time, but requires a dedicated server, immobilising captial and maintenance resources).
Ideally, it should be possible to use resources and incur their costs only when they are needed. This is the “Computing as a Utility” model.
Cloud computing is an approach to providing such automation services on the market, so that various enterprises can avail themselves of exactly what they need, on a pay-for-use basis. The provider distributes the cost among all the consumers.