Sorry I cant see the link to the image [removed?] can you post it again.
You can use a free file host like the link below if you have no space to host it http://tinypic.com/
Using the flash does fill in shadows on close by subjects which helps a lot if say you are facing the sun and the subject is in shadow or you are at a party in a poorly lit room [be it natural or artificial lighting].Not using the flash would either render the subject dark with a correctly lit background or if you use the subject as the exposure reading instead of the background [spot reading] a well lit subject but an overlit or "burned out" background.One disadvantage is that if its a busy fast moving background i.e. racing cars/busy street you will see movement or blur in the unflashed area of the image i.e. the background due to the longer exposure required for flash but this can be used to good effect if done correctly.