Maybe not what they meant, but Rust sometimes makes it tempting to just copy things rather than fighting the borrow checker. Whereas in C++ you're free to just pass pointers around and not worry about it until / unless your code crashes or gets exploited.

Speaking authoritatively from my position as an incompetent C++ / Rust dev.

I see. Fortunately, I'm aware of that and I don't use clone (unless I intend to) as much. Borrow checker is usually not a problem when writing scientific/HPC code.

Because passing pointers isn't as ergonomic in Rust, I do things in arena-based way (for example setting up quadtrees or octrees). Is that part of the issue when it comes to memory bandwidth?