One of the main efficiency gains is in massively reducing the number of round trips required to do a series of operations.

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5.5. Multiple Commands in Progress

The client MAY send another command without waiting for the completion result response of a command, subject to ambiguity rules (see below) and flow control constraints on the underlying data stream. Similarly, a server MAY begin processing another command before processing the current command to completion, subject to ambiguity rules.

IMAP already supports batching.