Using ChatGPT to rewrite your existing pages into blog posts won't help your SEO. Google wants fresh, original content with new information, not rephrased versions of what you already published. Duplicate or near-duplicate content provides no value and can stall your rankings.
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Lots of clients tell me they're tempted to use ChatGPT to write all of their content, and what they do is they tell ChatGPT, go to this page on my website and rewrite it as a blog. Here's why you don't want to do that. Google is looking for new and interesting content. It wants content written by human beings, and it wants content that is different than what's already on your website. If you're tempted to do things like this, what will happen is you will have already said what you've already said on your website, and it will be the same even though the words are in a different order, or you might have a different heading, effectively you're saying the same thing. And when you do that, you're not giving Google something new to chew on, and so your SEO won't grow.