I might have not made my position publicly clear about grammar study in language learning, but I will now.
I'm against it. I think it is, in most cases, a waste of time.
Grammars are very valuable. Study of grammar brings a deeper understanding of the language. It is just that knowing it has very little effect on your comprehension and your output. That's it.
If you already know the language well, learning grammar will boost your ability to reflect over sentences. It will give you ability to discuss the language with other people.
It will probably make your reading or listening skills better, but its effects are minor comparing to simpler things like reading for your own enjoyment.
But if you enjoy learning grammar, thought, you'll be killing 2 birds with 1 stone. If you fall in this category, for all means check this link:
How often? は日本語で何？
3 weeks ago