While the the best of them offer surprising amounts of flexibility, they also impose stringent enough restrictions to page design that you shouldn't be able to create a really bad looking site using one of these services. Typically you can get a Mysite.servicename.com style-url with no commerce abilities for free from one of these services; you have to pay extra for a better URL and the ability to sell. One issue to consider is that if you eventually outgrow one of these services, it can be hard to export your site to a full scale advanced web hosting like Dreamhost or Hostgator. If you know that's where you are eventually going, it may be better to skip the sitebuilder step.
By creating a website, you are creating an online presence. This allows you to connect with people that you might not otherwise be able to reach. Whether you’re making a basic website with contact information for your small business or medical practice, creating a landing page for your freelance work, a multi-page experience for your wedding photography business or you just want a place to blog about your thoughts on food, having a website will give you a dynamic advantage.