Yes, it is useful. For example, if you want to bootstrap a language implementation from the smallest possible subset, with a very trivial interpreter, then usin

Yes, it is useful. For example, if you want to bootstrap a language implementation from the smallest possible subset, with a very trivial interpreter, then using Y-combinator as a way to implement recursion is reasonable (after all, performance does not matter for the bootstrap phase). See an example of such a use in https://github.com/combinatorylogic/mbase/blob/master/src/l/boot/boot.al https://github.com/combinatorylogic/mbase/blob/master/src/l/...