https://hydrogenaud.io/index.php/topic,125597.0.html

so, improvements in the low bitrate space (32kbps and below?) which xHE-AAC was previously superior, but according to the developer:
“should I re-encode my music library again or likely no improvements for ~128kbps opus?”
“The main focus for 1.5 was on real-time communications, so no need to re-encode your library.”