S2C should make it possible to disable exactly once semantics by the leader. This might be needed either when the state machine itself is idempotent, or its design doesn't require the exactly-once semantics. For those cases, disabling exactly-once should be beneficial, because otherwise S2C would force commands ordering by the leader and latency can add up if the count of out of sequence commands is high.
S2C should make it possible to disable exactly once semantics by the leader. This might be needed either when the state machine itself is idempotent, or its design doesn't require the exactly-once semantics. For those cases, disabling exactly-once should be beneficial, because otherwise S2C would force commands ordering by the leader and latency can add up if the count of out of sequence commands is high.