Everything that an audience is viewing is content that they will respond to. In other words a blank page is something that we see just as much as a page filled with other visual elements. Whitespace can be used by designer to create asymmetrical balance, lead the viewers eyes through a design, create contrast and many other things that can help a design look professional.
On This site the whitespace and the shape of it is used to create not only a dynamism but also to create asymmetrical balance. On the other hand if the whitespace is ignored then it can cause a site to look amateur. For example in my opinion on Dogs.net the space between the header and the body of its text looks so bad it seems like a mistake.
Remember that white is just the default value of a web page and of most paper but that does not mean it is not a value. In RGB (Red, Green, Blue) which is the color gambit of computer monitors the value is expressed as #FFFFFF. So it should be treated as a value.
Therefore, make sure that when you create a design remember that your audience is seeing the negative space as well as the other content that you are uploading.