In principle The Sufficiently Good compiler can do everything up-to the as-if rule. In practice most of the time the temporary object is optimized away. But if

In principle The Sufficiently Good compiler can do everything up-to the as-if rule. In practice most of the time the temporary object is optimized away. But if the object is very large or the copy has side effects, thing are harder or impossible and those are probably the times where you need the optimization the most.