Agility lives off the automation of the same repeating activities: build, test and deployment. Only when these activities run at the flick of a switch is the way free for short release cycles. If the activities of build, test and deployment take a number of days then the temptation exists to do this as seldom as possible.
On the other hand, when these activities run automatically and quickly then, per day, more features can be brought to go-live. A pre-requisite here is mostly that all activities required can be initiated from the command line (or shell) or, as it is termed today, can be scripted. Only in this way can large and complex overall solutions with their internal dependencies be administered in a fully automated way by dedicated continuous integration (CI) tools such as Jenkins.