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/internalClusterTest/java/org/elasticsearch/index/FinalPipelineIT.java
@Override
    protected Collection<Class<? extends Plugin>> nodePlugins() {
        return List.of(TestPlugin.class);
    }
    @After
    public void cleanUpPipelines() {
        client().admin().indices().prepareDelete("*").get();
        final GetPipelineResponse response = client().admin()
            .cluster()