For what kind of concepts do we really need an analogy? Literature suggests that analogies are helpful in teaching and learning science concepts. But every concept can not and should not be taught using analogies as there are some concepts that can be better taught using examples and learning by doing .

My question is " for what kind of concepts do we really need an analogy ?"
Answers may include a reference to a piece of literature / some insights from teaching experience /blogs etc.
Loosely defined, analogy is the process by which "novel situations and problems can be understood in terms of familiar ones". By this definition, a number of cognitive scientists would and do say that analogy plays a role in acquiring just about any new concept - they would say that especially examples and learning by doing are means of refining one's ability to map from the known to the unknown and uncover the latter's structure/properties. In addition to the linked book, which offers a collection of papers/essays in cognitive science on analogy, you could check out Douglas Hofstadter's Surfaces and Essences: "Analogy-making, far from happening at rare intervals, occurs at all moments, defining thinking from top to toe, from the tiniest and most fleeting thoughts to the most creative scientific insights." In the appendix there is a very long list of scientific publications supporting his assertions.