Compiler optimisations certainly play a large role, but they're not the only thing. Tracing-moving garbage collectors can trade off CPU usage for memory footprint and allow you to shift costs between them, so depending on the relative cost of CPU and RAM, you could gain speed (throughput) in exchange for RAM at a favourable price.

Arenas also offer a similar tradeoff knob, but they come with a higher development/evolution price tag.