Not sure what materials your hoping for, but I've pointed codex at pprof application endpoints and just told it to identify hotspots and propose lowest hanging fruit/highest ROI items to fix, which I then approved it to open PRs for. Reduced application CPU usage by ~30% on loaded servers.

It's not magic. Fairly obvious oversights that I or someone else on the team could've found and fixed if we had looked, but it was never a business priority so we never did until I curiously spent 5 minutes asking it to do it for me.