Since most of us stand somewhere between five feet and six-and-a-half feet off the ground, that's the height from which we shoot most of our photos. Easy and convenient, but predictable. You'd be surprised how few people don't bother to kneel down or lay on the ground to shoot a photo--even when the subject (like Sailor the cat) happens to be at ground level.
Getting low works particularly well with children and pets because you're shooting at their eye level, which not only makes the photos more intimate, but makes the subjects feel more engaged with your camera (although to be honest, Sailor was far more engaged with the wild suburban jungle than with me). But getting down low provides an interesting and fresh-looking perspective with almost any subject and really adds nice variety to your photos. Some cameras (like my Canon point-and-shoot) have an articulated LCD screen that makes it easy to see the image even when you're laying flat-out on the ground because you can aim the screen up at a comfortable angle (it's tough to use that peep-hole viewfinder when you're laying on the ground). I love that articulated LCD, by the way, and it's a feature to keep in mind next time you're looking for a new camera.
Get down low, get up high, do whatever it takes to make your photos interesting.