It makes a big difference when a language spec (such as Scheme) requires it. If only some implementations have it, and you can't assume it when coding, then it

It makes a big difference when a language spec (such as Scheme) requires it. If only some implementations have it, and you can't assume it when coding, then it's "just an optimization". https://en.wikipedia.org/wiki/Tail_call#By_language https://en.wikipedia.org/wiki/Tail_call#By_language has a list.