A regular pattern every programmer has to deal with sooner or later is fetching data from a network resource, and reusing that content in their application regularly. This could be configuration data, rows from a database, xml or html content. Much of this fetched content does not change while an application is running for a short time; it may not even change for several days. [On computers with large and stable pipes to networks, fetching the data from an external source is not necessarily that expensive (but even then it is dependent on the size of the content)]
On mobile devices, like the iPhone, caching can be very beneficial, because fetching data from a networked source is considerablly more expensive than on a desktop computer: the data transfer rate is slower, leading to slower retrieval of content; network connections can be transient as the user of the mobile device moves in and out of areas of network coverage; and there is usually a cap on mobile plans for bandwidth.
Sarofax Technical 