What is the essence of idempotency of requests and why is it an important characteristic in systems?

Request idempotency means that executing the same request multiple times results in the same outcome and does not further alter the system's state after the initial call.

This is important because in distributed systems or during network failures, requests may be repeated. If a request is idempotent, a repeated call will not cause undesirable side effects, such as double charging or creating duplicate records.

Example: The HTTP GET method is idempotent — requesting data does not change the state. PUT is usually idempotent — updating a resource with the same data will not change the result upon repetition.