I personally don’t think site builders will ever replace web designers/developers completely. Most site builders are targeted at small businesses and could never meet the demands required for larger businesses with all their complex requirements. I think Shopify plus is the only product trying to take on the larger CMS platforms right now (e.g. Magenta, Demandware) in the eCommerce space
The front end is what your visitors will see when they come to your website. Many of the tasks performed on the back-end will be visible on the front end, such as theme customizations, plugin functionality enhancements, and content publication. Actions can also be performed by you and your visitors directly from the front-end of the website, including commenting and social sharing.