When does 32GB of RAM actually help with compile times?

Only if your system is running out of memory and hitting swap, which grinds everything to a halt. For typical React or Rails apps, 16GB is usually plenty — check your memory usage during a build; under 80% utilization means more RAM won’t help. 32GB makes a real difference for heavy users like C++/Rust/Android developers with large codebases, Docker/VM users, or monorepo workers.