Firstly, it's fabulous as a toy. You draw 3D models of pretty much anything you want (I just put together some quick examples as soon as I downloaded):
Clearly, you don't have to be a mechanical-drawing expert to draw the basic stuff, like buildings, simple objects around you etc.
But the real value lies beyond this. Artists at Google are busy putting together famous buildings around the world on 3D models and uploading them to Google Earth - another fabulous tool by Google. In essence, you can draw 3D imagery from around your home, office, or places you like and combine it with the real life sattelite-maps.
Look at this one from Google:
Hats off to Googi, again!