JIT compilers can't compensate for poorly organized data. Ultimately, understanding these low-level concepts, affect high-level algorithm design and selection.

Watching the Andrew Kelly video mentioned above, really drives home the point that even if your compiler automatically optimizes structure ordering, to minimize padding and alignment issues, it can't fix other higher-level decisions. An example being, using two separate lists of structs to maintain their state data, rather than a single list with each struct having an enum to record its state.