Compositing and masking techniques give you another level of creative control. You can create unique effects by blending the colors in overlapping objects. Fireworks has several blending modes to help you achieve just the look you want, from Darken to Saturation to Tint.
Another way to create a unique effect is to create a mask group. With masking, you can use a path object or an image object to create a cut-out effect on an underlying image. For example, you can place an elliptical path object on top of a photograph. Then select the path and the picture and create a mask group. All areas outside the ellipse are effectively cropped, leaving only the part of the picture inside the ellipse.
You can create all sorts of interesting effects by changing attributes of the objects in the mask group. The possibilities are endless.