Kafka offset - external storage vs consumer.committed(partition)

I'me trying to use "Consumer external offset management" implementing ConsumerRebalanceListener. I'm asking : Why does not use for onPartitionsAssigned calling consumer.committed(partition) to get the last committed offset instead of to read it from the same external storage? As I can see - kafka broker maintains itself this offset for each partition. If we persisted last successfully reading message offset on external storage in @KafkaListener - the value of this offset will be exactly getting by consumer.committed(partition). Of course we have: enable.auto.commit = false