Grammar at its best promotes clear communication but more often is used as a social tool of control and exclusion. When you are already talking to people within your in-group, that impulse isn’t necessary.
If the game is wearing a $20k watch or understanding the covert signs of status that you might find in a particular community, that's something different.
When we speak about the grammar for a language/dialect we imply a prescribed "correct" grammar for a particular community of speakers.
Not prescribed, rather observed. At least in English where there is no language authority and dictionaries present usage.
The situation is even stranger in Norway where there is a prescribed form but where dialects have essentially equal rights so that the prescription really applies only to formal written Norwegian.