Yes, clarity and grammar matter. For example, with your lack of capitalization, I wouldn't know if you were trying to help your Uncle Jack off a horse or your uncle jack off a horse.
I'm a fan of learning grammar well, to be clear, and wish mine were better, but this is not a good argument for grammar mattering.
Even scanning text is jarring when the rules aren’t followed, takes extra time to comprehend and adds to the minor irritants of daily life and will have people judging you, even subconsciously, as unintelligent.