This subject is again begin discussed at a thread on our LingQ forum.
My comments were as follows.
I agree with Evgueny. The issue is not whether to study grammar or not, but rather how much to focus on grammar and at what stage in one’s learning. Vey experienced language learners, and analytical people with a taste for grammar, may want to spend more time on grammar even at the beginning. For most people, and certainly for me, I find that grammar is hard to digest, especially at the beginning. As I progress in the language, listen and read more, have more words, in fact have more experience with the language, I am better able to digest the grammar since I have already come across many of the phenomena described by the grammar, as Rae says.
Often the language text book, or even the commercial language courses, will tell you that in this lesson you will learn the “subjunctive” or something. I don’t find that to be the case. All that lesson does is explain a particular point of grammar and give you some examples. You will not learn this form or pattern until much later, but you now have a place to go back to over and over.
The ideal grammar lesson is what Evgueny has done in the target language. I can go back to these over and over, and stay in the target language. This is more difficult to do at the beginning where some light description of the grammar in a language that is known to the learner is probably useful.
So, in my view we need to mix input with some grammar help, and the amount will vary according to the tastes and interests of the learner.