When you're inserting content into your newsletter, website or blog, you're often copying it from other documents. I suggest you always compose in Word (or similar) to take advantage of its spelling and grammar-checking functionality.
Your formatting in Word may not be the same as your default formatting in these various applications. While there are a raft of applications that make it easy now to do your own newsletter, website and blog, most of them are converting your content to html code in the background. When you copy in text that is already formatted, you're possibly creating problems behind the scenes. As well, you'll end up with differing fonts and sizes that all have to be corrected before you publish.