In Ubuntu and Unix generally, there is a superuser named root. The superuser can do any and all tasks, therefore daily work as the superuser can be dangerous. It is possible to type a command incorrectly and destroy the system. Ideally, you run as a user that has only the privileges needed for the task at hand. In some cases, this is necessarily root, but most of the time it is a regular user.
"If you disable the sudo password for your account, you will seriously compromise the security of your computer. Anyone sitting at your unattended, logged in account will have complete root access, and remote exploits become much easier for malicious crackers."
More information can be found at Ubuntu Community Documentation