Short answer: The writer 'knows' his work, and is less likely to spot a problem. For typos and certain kinds of thinkos, it may help the writer to change the typeface severely, eg., from a serif face to a grotesque face. But this is less helpful for awkward constructions in grammar and subtle ambiguities of meaning.
For punctuation, I think the author of a stand-alone work should reign supreme. For articles and essays in newspapers, magazines and such, having a consistant punctuation style can help the reader and help the publication to present a uniform product, but even here I think the author should be allowed some occasional latitude.
