Step Function When to use Iterator pattern and Map State

if we want to "iterator" to list, Map State supports concurrency and we set it to 1 then when to use the iterator pattern? https://docs.aws.amazon.com/step-functions/latest/dg/tutorial-create-iterate-pattern-section.html

The iterator pattern will be beneficial for long-running tasks, if we check lambda execution time, gracefully shutdown it, and resume the execution by checking flag in choice state.