Final answer:
Instant retrieval systems are used for the playback of conversations after calls have been completed, enabling review and analysis for various purposes.
Step-by-step explanation:
Instant retrieval systems are designed to allow the playback of a conversation after the call has been completed. These systems ensure that conversation details are not lost and can be reviewed for various reasons, such as quality control, training, or legal purposes. For instance, a condensed transcription of a conversation can be played back immediately after the recording session ends. This instant playback feature is quite beneficial in situations where recalling specific details is necessary, like when analyzing a conversation as part of a mnemic system for better recall and understanding.