When I marked papers as Graduate Assistant and then as a teacher, I would hand back any papers that had more than a few spelling or grammar errors. My rationale was that if the student could not be bothered preparing the paper properly then why should I be bothered marking it. That was many years ago. It felt like a losing battle then and feels like one now when I review books or read student papers that are full of errors. The modus operandi appears to be it is easier to make the mistake then apologize. The problem with that is by the time you come to apologize it may be too late to rectify the damage you have caused by making a poor first impression, and reputations are often built on the competence of the first action not the reaction. In publishing, that leads to reduced sales, and avoidance of your work by potential readers; for students, that could be the difference between an A and a B. That is why hiring a proofreader is important, even if just to put a last objective pair of eyeballs on a piece of writing.   Your final point on your writing checklist then should be the first item you write down: proofread!