Uses of modal windows are pretty normal in modern web design. Usually one have to click on “x or close” button, place in corner to exit the window.
Some expert designers have already used this modal window in such a way, users need not always click the “x or close” button to exit the modal window. Instead, s/he may exit the modal window by clicking the area outside without anything else. It is as simple as it is. No need for clicking specifically on “x” mark or “close” button.
Doing so, we can save at least a few millisecond of user’s time and make them happy. Personally, I often click the background of a modal window to get back to main screen. So, I suppose, focusing on this will have positive effect on a webpage’s overall user experience.