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/main/java/org/elasticsearch/ingest/IngestDocument.java
* If the path value is a string, a base64 decode operation will happen.
     * If the path value is a byte array, it is just returned
     * @param path The path within the document in dot-notation
     * @param ignoreMissing The flag to determine whether to throw an exception when `path` is not found in the document.
     * @return the byte array for the provided path if existing
     * @throws IllegalArgumentException if the path is null, empty, invalid, if the field doesn't exist
     * or if the field that is found at the provided path is not of the expected type.
     */
    public byte[] getFieldValueAsBytes(String path, boolean ignoreMissing) {
        Object object = getFieldValue(path, Object.class, ignoreMissing);
        if (object == null) {
            return null;
        } else if (object instanceof byte[] bytes) {
            return bytes;
        } else if (object instanceof String string) {
            return Base64.getDecoder().decode(string);
        } else {
            throw new IllegalArgumentException(
                "Content field [" + path + "] of unknown type [" + object.getClass().getName() + "], must be string or byte array"
            );
        }
    }
    /**
     * Checks whether the document contains a value for the provided templated path
     * @param fieldPathTemplate the template for the path within the document in dot-notation
     * @return true if the document contains a value for the field, false otherwise
     * @throws IllegalArgumentException if the path is null, empty or invalid
     */
    public boolean hasField(TemplateScript.Factory fieldPathTemplate) {
        return hasField(renderTemplate(fieldPathTemplate));