Why CSS Frameworks?
CSS frameworks or libraries are intended to solve the same problems as any programming library - to make certain tasks easier, and to standardise repetitive work. They grew from various front end developers realising they were doing the same cross browser resets and layout setups over and over again, who refined these standard parts of their processes and released them publicly.
These frameworks can be, and have been, used to layout production sites, but they are perfect for prototyping and 'undesigned' areas - the administration pages, web GUIs and intranets that are often left entirely to the developer in terms of the look and feel. They offer easy and straightforward ways of putting together better looking and easier to use sites, by encouraging the use of some basic principles of design.