If you decide to change the look of your desktop, bear in mind that it is only about pictures and images. There are the usual icons which you can personally design yourself if you are into it and but as a whole, they are all about imaging and packaging them uniformly to gain the nod of people who want them for distribution and for their own.
Apparently, you may wonder why apply a theme when you can always change the desktop image using the default use of control panel and display setting? This way it eats up lesser resources and the need to modify and select the settings is easier. With a Windows XP system, you can even apply the desktop settings of a Windows Vista so why bother to use different themes?
Surely, this depends on how technical a person using a computer may be. For the basic to standard people, it is easier to change a theme with a few steps. Some people are apprehensive when it comes to tinkering around with the other stuff and commands in a computer and you really cannot blame them. For all you know they will panic as soon as they make a false move to which the whole system may eventually go haywire.
Some would call it a basic and logical understanding while others may not. Whatever the case may be, it just remains that theme changing is applied by people who are fascinated at the things they can do with their computer. But to others, it is as simple as exploring other things that they can do, and this includes a simple visit to the windows control panel.