A Joomla ! website's security is one of the most important issue for a webmaster. Indeed, it is not enough just to work hard on a project, sometimes on local server, to run various tests, to set everything up, then to put it online and congratulate yourself.
As a matter of fact, the security of a Joomla! site (or of any other website) is more or less a daily work that needs to be taken very seriously.
A properly secure website ensures the durability of your projects, it reassures your users and, most significantly, that will spare you the trouble of having to work many hours if your site's been hacked. Spending some time on your site's security every now and then is much preferable to sleepless nights in case of security issues.