Nothing comes for free in our world. There are a number of disadvantages to a free blogging platform. There are rules laid down by each platform that you need to observe. The domain name of your blog appears to be a subdomain such as "myblogname.wordpress.com" or "myblogname.tumblr.com". There are limited functionality, plugins, and theme selection you can make to your blog. Last but not least - usually, free platforms limit the opportunity of monetizing your blog. I strongly suggest you start your blog using a self-hosted WordPress.org (as what I've covered in this guide). Besides overcoming the limitation of the free blog, the potential growth of your blog is limitless.