The website service host allows you to display websites in tabs. Website service hosts are useful when you have a site that refuses to run in an iframe (read: a tab) . If your site is able to run in an iframe, you do not need to use a website service host, and you can just use the Web applications tab type.
The website service is required to create the underlying resources for your virtual browser in your sandbox. Generally, you should always have a website service created for each site that you would like to view in your virtual browser. A virtual browser in a challenge by itself will not function without this website service configuration in your sandbox.
Each sandbox is subject to a limit of 15 containers and website services combined at any given time. This limitation helps ensure optimal performance and resource allocation for all users.