There is a school of thought when it comes to learning a foreign language: proper grammar is not necessary. The reasoning behind this is that even natives do not speak their language with proper grammar and their message is understood. As long as your message is forwarded and understood, that is all that matters.
I agree up to a certain level. Indeed if you are a beginner and you only need your target language for survival, you probably don't know learn grammar in a deep level to ask "how much is this?".
But to delve into a conversation deeper I believe that it is necessary to learn proper grammar. Yes, even if you speak your target language without proper grammar, chances are, natives speakers will understand what you trying to say.
But this creates a problem. If you do not use proper grammar then you are relying on someone else to interpret what you are trying to say.
For example (Vietnamese):
1. Tôi không bao giờ đi đến Việt Nam.
2. Tôi chưa bao giờ đi đén Việt Nam.
Both of the above sentences mean " I have never gone to Vietnam. But the first sentence with "không bao giờ" means I have never gone and never will go to Vietnam. The second sentence with "chưa bao giờ" means I have never gone to Vietnam but there is a possibility that I may go one day.
Another example (Romanized Korean):
1. Joe wattsuhyo
2. Joe neun wattsuhyo
Both sentences mean "Joe is here" but the second sentence also has an inference that has this type of feel: "Joe is here, but I am not sure about anyone else." That one syllable neun is very important grammatically and allows for more precise communication.
In the beginning if it probably OK to not have precise grammar, but I think for people who have higher aspirations for their target language other than for survival or traveling, some time and effort has to be spent learning grammar.
Totally agree with you 100%.
I can give some concrete examples. I know many Japanese and Korean students of English that claim that they "already know grammar", but in reality they cannot even construct a sentence. Knowing grammar makes constructing sentences easy. Grammar is essential for languages, especially the languages with significant 'language distance' like KOR-ENG and JPN-ENG.