[oulipo2]

It could still be useful if the spec is roughly as hard as a simple implementation, in case you have automated methods to find more efficient implementations, guided by the constraints of the spec

[auggierose]

Which is still a case of the spec being simpler than the implementation (you are after) ;-)

Very often, the spec is indeed just a very simple implementation. Often you can make the spec especially simple if there are no constraints on the resources it can use, at times even infinite ones.

[Animats]

Right. Databases can be modeled as linear search over huge arrays, for example.