Grammar is the whole system and structure of a language. It is used to discipline the language by using word structure, parts of speech and formation of words. It is helpful in the arrangement of words and phrases to create a well-formed sentence in a language.
If you don’t use proper grammar then you can’t make understand the world about your thoughts and they will ignore you.
Grammar and language vary with the place and the audience who is hearing it. That’s why your thoughts and ideas are not appreciated most of the time because you haven’t ruled of grammar according to place and audience.
Suppose you are with your friend’s group and you are sharing about you your last vacation which was full of adventure, and you started saying like “good morning ladies and gentleman, today I am going to share about….”, this will totally go wrong and your friends will start ignoring you.
Similarly, if you are sitting in an interview session and the interviewer asked “tell me about your hobbies” and you started saying like “see dear I love…” this will also go totally wrong. The interviewer will find it very unprofessional and directly ignore you.
That’s why I have explained it earlier that language and its grammar vary with the place, situation, and audience.