With the advent of e-products, online retailers, and the explosive growth of Web business, metadata has grown exponentially and has increased both in complexity and importance. A single title that originally carried a single print record suddenly became available in multiple formats, each with its own associated metadata. Typically, there are 30–40 fields of metadata required for every digital product in active distribution. Even for smaller publishes with inventories of fewer than 2,000 titles, the exposure can run to 50,000–100,000 data points.
In addition, online markets began demanding a variety of descriptive and transactional metadata. This is metadata that then controls and enforces the rights, permissions, and distribution rules set by the publisher. Furthermore, with the advent of search engines, metadata became the key to discoverability. Precision in writing descriptive metadata became critical.
Source: Reflections on Metadata