**Neither a teacher nor a native speaker.**
I think grammar is very important.
However, it also depends on whom you speak to.
If it's a beginner, you will not need to use "perfect" grammar because the person cannot handle it.
Whether you say:
I will leave tomorrow.
I am going to leave tomorrow.
I'm leaving tomorrow.
I leave tomorrow.
anyone would understand you.
Furthermore I cannot really understand how they can suggest to forget the English grammar.
Everything is grammar.
Does he play well?
Okay, now let's forget the grammar.
Plays he good?
Yes, it's an extreme example, although almost everyone would understand you, but it's horrible.
(You are new in a town.)
Some guy: Hello, are you new here?
You: Yes, I've been here for a month.
You: Yes, I'm here for a month. -> No grammar.
Of course answer 2 can be correct, but let's say one month ago you arrived and you're still here.
In that case no one can know what you mean if you say it wrong.
Let me ask you something:
Where exactly do you feel very hard when using correct grammar?
Of course there are situations where you must decide if it's worthy to use correct grammar.
Let's say: "He plays better than I. " "It's I." "I too."
If you're a rebel, stick to them.
If you want to avoid questions, use what most people use.