[torginus]

Not really. Tasks can be zero garbage, IEnumerable cannot. A 'task' in C# is just something that has a GetAwaiter() method, which gives you a callback on when something has happened.

This is how ValueTask is implemented in newer .NET versions which is a struct, but you can roll your own.

[jayd16]

Yes really. It's huge effort to make this happen. ValueTasks bring their own gotchas, like not being able to be awaited multiple times. Yielding from an existing IEnumerator is free while every await is a chance to cause garbage with a new awaitable. Even Task.Yield() allocates garbage (in Unity at least) and trying to get Unity lifecycle events as cheap and safe awaitables is not really feasible. At least at the moment.