The HTML Exporter plugin is incredibly useful, way more useful than you might at first think.
It allows you to save WordPress pages or posts as static HTML. As a copywriter, you could use a web page building tool for WordPress such as Optimise Press to create a sales page for a client within WordPress.
Then export it as HTML and send it to them fully done.
As a consultant / web designer, you could send the HTML files (which would open in the receiver's browser) to your clients to show site progress without having to publish pages of a not-yet-ready site.
As the owner of a WP membership site your sales page could be less integrated with WordPress itself, so no need to install a pile of unnecessary plugins if you have multiple sites. That means is there's no need to buy multi-site licences for plugins or themes that allow you to create sales pages and membership sites. That's a BIG money saver when looking at some of the expensive products out there.
As a consultant / web designer, you could create a one page site in WordPress for an offline bricks and mortar business, containing contact details, opening times, and what they did.