Let's say you're at a concert, or a show, or a sporting event or maybe you're seeing a street performer do a spontaneous trick! You love to clap, everyone does! Well okay or to be fair maybe you're a person who doesn't enjoy clapping at all. But that's not really the point at all. The point is that its a time to show appreciation at the thing you're seeing, but wait! your hands are occupied! Oh no! Maybe you're drinking some sort of beverage, or holding a loved one's hand or who knows?! whatever the reason, you cannot clap, so what do you do?
Well you've got a few options: shout a "woo", or a "Yeah!", or a wolf-whistle. now I can whistle pretty well, but by no means can I do the ear-drum-splitting, two-fingers-stuck-in-the-mouth, wolf whistle that gets attention and shows appreciation. But if you can, go for it!
There also shouting "Yeah!", which I like, but I think it has some drawbacks: a) it puts some unwanted strain on the vocal chords b) I don't believe you can "yeah!" at quite as high a frequency, so if everyone else is making a lot of noise you might get drowned out in the ocean of noise.
Here we come to the final choice: The Woo. The double 'o' vowel alows for a structure giving to a greater range in frequency: you can mold the sound up and down as you yell. Making it quite versatile indeed.
But it really doesn't matter what you do, so long as you're having fun.