It will be very efficient when the async operations are few, and slower. It will not be very efficient when the async operations are many and fast.

That's because the await keyword itself blocks the main thread every time a function call is made. It has to because the `await` keyword is defined to return to the event loop and resume processing only during the next "tick" and after other queued ticks have run.

For a large collection the overhead on the event loop can be calculated as: COLLECTION_SIZE * FUNCTION_CALLS_PER_ELEMENT. Since function calls per element goes up as you wrap layers of helper functions, even with this library you would face a strong perverse incentive to avoid using (async) function calls or nested iterators (if at all possible) when handling large collections, especially with high desired throughput, especially in situations where you want the event loop to stay unclogged so that you can, for example, redraw the UI.

In other words, put on the stack at the same time but not a different thread.

Do correct me if I misunderstood though.