Fresh, well-written and relevant content will enrich your website visitors experience. But if you rush your work by trying to throw together content without proofreading and spell checking you will not look very professional.
Knowing that your blog is a huge part of your overall online presence you need to make sure the basics are addressed and spell check is definitely a basic. Typos and bad grammar are very distracting. Making your readers re-read sentences and even paragraphs is not only inconvenient for your reader, but also may cause them to question your thought process and dedication to your writing.
Different people write differently. Some carve every word and move very slowly, picking just the right word before they move on to the next. Others choose to jot down their thoughts right away and then polish the sentences afterward. Whichever way that works best for you is fine, just make sure you proof your work at least twice before publishing.
You can read your content over slowly or read it backwards to make sure words are not duplicated or misspelled. You should also read your content out loud or have someone else read the content so you know it reads well to another person.