I was looking at a flame graph of an ingestion workload with @dliappis, and it looks like we parse the JSON representation of the index request twice when a document has both a pipeline and a final pipeline.

It's hard to know how much we would save on this benchmark since not all data streams in this benchmark had both a pipeline and a final pipeline, but the cost of parsing index request into maps of maps via IngestService represented 4.06% of overall CPU time according to the flame graph, so this might not be negligible.
server/src/test/java/org/elasticsearch/ingest/IngestServiceTests.java
}
    public void testCBORParsing() throws Exception {
        AtomicReference<Object> reference = new AtomicReference<>();
        Consumer<IngestDocument> executor = doc -> reference.set(doc.getFieldValueAsBytes("data"));
        final IngestService ingestService = createWithProcessors(
            Map.of("foo", (factories, tag, description, config) -> new FakeProcessor("foo", tag, description, executor))
        );
        ClusterState clusterState = ClusterState.builder(new ClusterName("_name")).build();
        ClusterState previousClusterState = clusterState;
        PutPipelineRequest putRequest = new PutPipelineRequest(
            "_id",
            new BytesArray("{\"processors\": [{\"foo\" : {}}]}"),
            XContentType.JSON
        );
        clusterState = executePut(putRequest, clusterState);
        ingestService.applyClusterState(new ClusterChangedEvent("", clusterState, previousClusterState));
        assertThat(ingestService.getPipeline("_id"), notNullValue());
        try (XContentBuilder builder = CborXContent.contentBuilder()) {
            builder.startObject();
            builder.field("data", "This is my data".getBytes(StandardCharsets.UTF_8));
            builder.endObject();
            IndexRequest indexRequest = new IndexRequest("_index").id("_doc-id")
                .source(builder)
                .setPipeline("_id")
                .setFinalPipeline("_none");
            ingestService.executeBulkRequest(1, List.of(indexRequest), indexReq -> {}, (integer, e) -> {}, (thread, e) -> {}, Names.WRITE);
        }
        assertThat(reference.get(), is(instanceOf(byte[].class)));
    }
    public void testSetsRawTimestamp() {