A proofreader will uncover and correct your Web site's spelling, grammar and punctuation errors. Not only that, but they will also be able to correct the 'tone' of your site.
At first glance, incorrect or poor spelling, grammar and punctuation may not be an obvious cause of usability problems. But if a link is spelled incorrectly, it could be rendered useless.
A site with lots of spelling, grammar and punctuation errors will make your company look unprofessional.