The WTF domain is just an acronym that stands for the expression "what the feck". The expression can the further translated into an exclamation of disbelief or just plain insane situations.
For special news and entertainment media
Some news is just too good to be true, especially when it goes contrary to the general beliefs of people. Using a .WFT domain name for websites that deals in dishing out such type of entertainment contents will further increase your online presence and show how different from the norm your business.
For marketing purpose
The .WTF is a very unique domain name could also be used for marketing purpose as it translates to something unexpected and possibly insane. So let's say you decide a secret that could make people insanely rich or better their life for a price close to nothing, or maybe a discount on a product that is known to be fairly expensive on your website. Then you know such website does deserve the .WTF! Domain extension.
For personal use
The WTF domain name could also appeal to one's personal project for example if you intend on playing a prank on somebody online you could make use of this extension. The domain name also shows defiance and not conforming. If your website is all about this, you could also enjoy the use of this domain name.