Returning to the topic, after playing around with custom executors (quite new experience of concurrency), I came to decision that at my particular case it plays no role, while this ability to control execution is nice. What actually here made the difference for me is serializing execution (not using AsyncSequence, though). And together with initial confusion why OperationQueue still executes all at once, what I am looking forward now is either ability to control re-entrancy or inheritance isolation mentioned in the quote, which as far as I understand would allow to pass #isolated in such cases to control concurrency domain?