It can use less resources and can be faster than passing data between processes. There's really no reason to use multiple processes for IO-bound workloads, either, and even for some IO-bound workloads, a thread pool can be faster than processes.

The second you aren't just passing raw bytes around, you have to take into consideration what can and can't be sent between processes in Python, as some objects can't be pickled and thus can't be passed between processes.

You can concurrently load a lot more coroutines than processes and threads, as well.