The async/await model gives you exactly one guarantee: because the yield continuation is second class, at most one stack frame can be suspended, so the the amount of space that needs to be reserved for a task is bounded and potentially can be computed statically. This can be important for very high performance/very high concurrency programs, so I think the upsides can be more than the downsides in something like rust, C++ [1], and possibly C#. I still do not understand why async was deemed appropriate, for example, in python.
As an aside, there is a lot of confusion in this thread between general async operations and async/await.
[1] but of course C++ screwed it up by requiring hard to remove allocations.
> I still do not understand why async was deemed appropriate, for example, in python.
My best guess is that it's because of implementation limitations in CPython and likely other interpreters. StacklessPython is a fork of CPython with real coroutines/fibers/green threads but apparently they didn't want to merge that patch. Very disappointing, because async/await is a nearly useless substitute for my desired usecase (embedded scripting languages with pauseable scripts).
There is also gevent which is a library only coroutine extension which didn't require any changes to the interpreter itself. I'm also sure it would be easier to maintain and evolve if it was part of python core.
As an aside, there is a lot of confusion in this thread between general async operations and async/await.
[1] but of course C++ screwed it up by requiring hard to remove allocations.