I suppose it depends how hands-off the tasks are - I max out at 2 parallel sessions working on different parts and it's fairly exhausting once done. I can see the number of parallel work increasing if there's a good dev/test loop. But at $WORK, that's not usually an option.
So, hands-off meaning "just let the AI cook and don't check it"?
Either you follow everything it does, revise the plans, do the code review, manual adjustments, etc, or you run sessions in parallel, not being that attentive and constantly context-switch (also resulting in less attention I guess).
I fail to see the benefits honestly.