Aligning and Editing Simple Shapes
There are ten buttons in the Pathfinder palette: five to combine paths and five to divide/merge/crop paths (please note that the illustrations below were taken from Illustrator 10).
The buttons are: Unite, Intersect, Exclude, Minus Front, Minus Back, Divide, Trim, Merge, Crop, and Outline.
Here is a quick example of how to use the pathfinder on a simple set of objects.
As you can see, there are two ovals under a rectangle. By selecting the larger oval and the rectangle and using the Exclude button, you get the following:
Can you see how Exclude might save time making a yin-yang symbol?
In the same palette are the Align and Transform tools. You can use them to precisely tune an object or set of objects without using a grid. For example, in the yin-yang example, you could use the Align tool to center one circle inside another and to vertically align all of the circles.