In essence, pitch shift can make you sound like an alien creature, if you lower your voice by a few semitones, or like a chipmunk, if you dial it a couple of semitones up. The numbers may vary, but the concept stays unchanged. Say you want to accentuate a punch in a boxing match and it happens in slow motion or slows down right after the hit on screen. The hit, played back in normal speed, would sound inappropriate for such dramatic moment, as it has to be bigger and deeper to communicate the bone-shaking blow and suggest the consequences. If you pitch the sound down, it will become deeper and lower, but at the same time it will loose some of the "punch," the transient "edge" that makes it "feel" strong and painful. The easiest way around this problem is to layer the normal punchy sound and pitch down to a huge and low sound, retaining the punch and the hugeness at the same time. Another way is to crossfade the attack of a normal speed sound and pitch down its tail. There is no one right way to do things like that. I'd just go for what sounds good. Back to our swooshes, using the combination of filters and pitch shifting you can produce a whole range of "swooshy" noises from just one sample.
Sound source effects
One day, you may face the need to recreate a specific sound source, like a telephone,a public address system in a mall, an announcer at a train station or crackling walkie-talkie commands. It's difficult to transform clean recorded voices into those sound sources and make them sound genuine and believable. Most of sound source effects can be recreated by combining basic effects like distortion, EQ, reverb and pitch. However, in the real working conditions, the editor hardly has time to submerge into the elaborate process of effect chains.
Here’s a great piece of software: Audioease's "Speakerphone 2". It is, in fact, a chest of treasures with almost every sound source that exists in urban environments and interface to adjust individual parameters. Having this thing handy saves a lot of time, if you do sound design or editing for a picture.
There is one big thing which was left out from this brief overview and which is always with you. Your own voice. Human beings are capable of mimicking a whole lot of noises and, if you add some low-tech analog processing to your voice, like a cardboard funnel, metal pot or tin can, you'll be well-equipped to produce some unearthly sounds. Just try it and rediscover the fun of playing with your voice. You may be surprised at what comes out.