docs(common): describe behavior when reference changes (#42863)

PR Close #42863

packages/common/src/pipes/async_pipe.ts

@@ -61,7 +61,8 @@ const _subscribableStrategy = new SubscribableStrategy();
  * The `async` pipe subscribes to an `Observable` or `Promise` and returns the latest value it has
  * emitted. When a new value is emitted, the `async` pipe marks the component to be checked for
  * changes. When the component gets destroyed, the `async` pipe unsubscribes automatically to avoid
- * potential memory leaks.
+ * potential memory leaks. When the reference of the expression changes, the `async` pipe
+ * automatically unsubscribes from the old `Observable` or `Promise` and subscribes to the new one.
  *
  * @usageNotes
  *