The long-lasting debate of incidental learning of vocabulary vs. explicit teaching has led to a very reasonable conclusion - both methods complement each other and thus both are important for teaching of vocabulary.

My question is: in what circumstances one of these two methods would be more beneficial than the other. In particular, should we teach, for example, most frequent words in L2 explicitly while words that are rarely used in the language can be learned incidentally, i.e. through reading?