You should read every wiki page, bug report, and blog entry before you post it. Look at the whole document and make sure it says what you meant to say. Consider the people you are writing for and make sure they will understand you.
Another reason for reading your documents again is to look for typos and grammar problems. You will never catch them all, but you want to keep them to a minimum. If you have the privacy, reading the document out loud helps you find errors quickly. If something sounds wrong it probably is.