The mechanics of writing are the boring parts, the most obvious aspects of writing. These are all the things that you learned in grade school like spelling and capitalization (the kind of thing you had to do thousands of worksheets on, the things your teacher marked in bright red ink). While the basics may seem like they’re a little below you at the moment, they’re as worthy of your attention as the more involved aspects like research and citation.
The mechanics of writing play two parts: they aid in communication, and they show how much effort you’ve put into your work. The reader depends on small things like italics to identify the title of a book or a foreign word, and an apostrophe to differentiate between its and it’s. Even if the reader could figure out what was going on, typos and sloppy writing make it clear that the writer has no commitment to the work; if the writer has no commitment, why should the reader? As with anything else, the sum is only as good as the parts.