Maybe in a scenario where the existing codebase isn't already async-ified, as that can be a hassle because it often requires making many things async.

Otherwise, it's probably best to use asyncio over threads:

Why do we need asyncio? Processes are costly to spawn. So for I/O, Threads are chosen largely. We know that I/O depends on external stuff - slow disks or nasty network lags make I/O often unpredictable. Now, let’s assume that we are using threads for I/O bound operations. 3 threads are doing different I/O tasks. The interpreter would need to switch between the concurrent threads and give each of them some time in turns. Let’s call the threads - T1, T2 and T3. The three threads have started their I/O operation. T3 completes it first. T2 and T1 are still waiting for I/O. The Python interpreter switches to T1 but it’s still waiting. Fine, so it moves to T2, it’s still waiting and then it moves to T3 which is ready and executes the code. Do you see the problem here?

T3 was ready but the interpreter switched between T2 and T1 first - that incurred switching costs which we could have avoided if the interpreter first moved to T3, right?

http://masnun.rocks/2016/10/06/async-python-the-different-forms-of-concurrency/