It allows you to manage content ;)

In a nutshell, a content management system is an application or group of applications that allows an end-user to login securely to the "back-end" of a website and manage the collection of documents and how they are linked together (commonly called the navigation) that ultimately the public will view and use. A CMS gives an end-user the power and ability to control the links and page content of their website. There are as many arguments for and against CMS as there are CMS themselves.

thanks. But basically one can do the same things without a CMS as one can with a CMS? Okay..not trying to weigh in all the advantages and disadvantages hehe, but it's not like for blogs you definitely do need a CMS..or for bigger website you definitely do need one, but it all comes down to personal preference (and whether you think the advantages are bigger than the disadvantages)?