Your website looks unprofessional as the website address will appear on a subdomain such as yourwebsitename.weebly.com. Most of the time, free website builders are supported by advertisements and your visitors may see all sorts of irrelevant advertisements when they visit your website. The worst thing is, there's no guarantee of using free website builders which means your website can be shut down for no reason or your website is vulnerable to hacking due to poor security. These are among the risks of using a free website builder.