A complaint nearly guaranteed to be heard in the Freshman English classes is that grammar isn’t important. The argument often takes some form of, “Does this even matter? Can’t I just write the way I write? What’s the big deal?”
Check out the above video consider the ways in which we follow/ignore certain rules of spelling and pronunciation. Although languages are constantly evolving, nebulous entities, how are those who can operate with a set of conventions empowered?
In short — having a solid understanding of grammatical conventions puts you in a better position to express yourself clearly. And isn’t that the whole point of communication? (Answer: Yes.)