What happens when a C# method uses yield return, and what happens to resources if enumeration stops early?

I keep iterator bodies free of business side effects because partial enumeration means only part of the body may run. Consumers that manually obtain an enumerator must dispose it; foreach and LINQ operators normally manage that boundary. Exceptions are also deferred until the consumer reaches the failing part, so validation placed inside the iterator may happen much later than the initial method call. For asynchronous streams, IAsyncEnumerable<T> uses MoveNextAsync and await foreach, with cancellation and asynchronous disposal forming part of the contract. In production I document one-shot or resource-backed sequences and avoid exposing a lazy iterator after its required context, stream, or scope has already been disposed.