The code in org.hibernate.search.engine.impl.DocumentBuilderHelper.processMetadataRecursivelyForProjections could simply lookup the needed metadata to perform the requested projections by using the user provided projection names.

Instead, it seems to scan all possible metadata - including deep recursion into embeddable metadata - to find matches with the projection names.

I suspect this is mostly legacy as until recently we didn't have an explicit mapping for each embeddable attribute.