cPanel are HELM are web based interfaces which allow you to manage your domains on the servers. cPanel is used for Linux based servers while HELM is used for Windows server. Without hosting control panel, it is difficult to manage the web sites or domains on the servers. You can easily set up the servers using the web hosting control panels.
Web hosting control panels provide user friendly interface to manage the domains from clients end. Hence it would be easy for the clients to create the email accounts, upload/download files, change the files/folders permissions etc.