There are characters who believe they're so above everyone else, they might as well be flying. When you need to bring that "holier-than-thou," love-to-hate quality to one of your reads, there's nothing better than a pompous voice.
Arrogance, greed, and a sense of unshakeable moral superiority — in their mind, these characters stand so far above the rest that they might as well be a different class of being. But we know better, and we just refer to them as pompous, arrogant, conceited, and full of themselves. The pompous voice is the perfect weapon for when you need to give life to a haughty aristocrat, a greedy Wall street type, or anyone who is so convinced of their rectitude and worth that they might just pop like a baloon if you prick them with a needle.
There are many characters in film, animation, and video games that just love to believe they're on top of the world. The pompous voice is perfect to give life to wealthy, aristocratic characters who love to put on airs and belittle others. This voice type is also perfect for ads or commercials; audiences love it when a cocky bigwig gets tossed off their pedestal.
A pompous voice is defined generally by a (generally put-on) posh accent, very clear and distinct, slightly-nasally diction. If it sounds like characters are turning their nose down at others, it's because they are.