As the Weebly team states, the idea behind the platform is to make website creation available for everyone — not only programmers. Weebly remains one of the easiest-to-use site-building solutions out there. It delivers great tools for creating straightforward sites that serve specific purposes. Weebly is another hosted solution, which means that it takes care of housing your site and all the technical details related to it.
Just imagine Medium shuts down as did Posterous back in the days (which was a similar service). You will not necessarily lose all your content but all the SEO rankings you ever created. To get it right you need to publish on your own domain name and preferably on your root domain (www.yoursite.com/blog) and not a sub-domain (blog.yoursite.com). This has numerous SEO advantages.