Working with HTML/CSS/JS I can quickly build a business website. For extra I can build a backend in PHP, ruby on rails, nodejs, or any other server language.
My personal portfolio includes working on Twitter's website, Amazon, a feature for Nature magazine, and a business site for an aerospace machine shop and a couple food startups.
If you need just frontend development the service is cheaper and faster. This would be something like a static informational site or advertisement with mailing list sign up.
To include backend development increases the cost and time. Backend is needed for things like e-commerce and recording customer profiles beyond a simple mailing list registration. This is more work because backend is a separate code base and runs on a dedicated server.