> Common Lisp's string support certainly feels like it comes from a world where allocating memory is expensive, and something the programmer should be aware of, and have the option to reuse buffers instead of allocating additional memory...

We are still in that world. I do game programming, and am convinced that if a game programmer isn't aware of their memory allocations, then their game will drop frames. This is true today, even at 60hz (and things are moving towards 144hz, 240hz, and beyond). Reusing buffers is essential.

I think that being aware of when and where your memory comes from is the foundation of performance. The discipline of handling memory carefully tends to naturally lead toward making more performant decisions on everything else.