The CDATA structure isn’t really for HTML at all, it’s for XML.
People sometimes use them in XHTML inside script tags because it removes the need for them to escape <, > and & characters. It’s unnecessary in HTML though, since script tags in HTML are already parsed like CDATA sections.
Edit: This is where we open that really mouldy old can of worms from 2002 over whether you’re sending XHTML as text/html or as application/xhtml+xml like you’re “supposed” to 🙂