Placement new is just avoiding a copy. Without placement new allocating an object involves: a) Constructing the object on the stack b) Copying it to the heap

Placement new is just avoiding a copy. Without placement new allocating an object involves: a) Constructing the object on the stack b) Copying it to the heap With placement new you construct the object directly on the heap, thus avoiding a copy. It's purely an optimization to avoid a single copy. It's a bit surprising that Rust doesn't have it, given the focus on control over such things, and that it had an experimental 'box' keyword for this at 1.0. edit: To be clear, the extra copy is not guaranteed - compilers can elide it. In order to help the compiler do this you can look at crates like boxext, which provide extension methods on Box that help the compiler to remove the copy. But placement new guarantees this.