Here’s a helpful snippet to measure the impact of this change (taken from Excessive memory use during eval of a particular flake - #4 by xokdvium):
$ NIX_SHOW_STATS=1 NIX_SHOW_STATS_PATH=stats.json nix eval <ref> && jq '.gc.totalBytes' stats.json
Doing my own test, I saw my configuration evaluation drop from 3.7GiB to 2.4GiB. That’s an incredible change!