I think the confusion comes from the fact that Steve would consider code written by someone who "hasn't written much Rust" to be "beginner code," so he meant ex

I think the confusion comes from the fact that Steve would consider code written by someone who "hasn't written much Rust" to be "beginner code," so he meant exactly what the book says. I would agree that people getting the hang of Rust shouldn't worry too much about this, but that production code that deep clones buffers when it could use references is badly written (then again, it may not matter at all!).