The Spin tool is a great tool for modeling objects you might make on a lathe quickly and easily.
Lathe objects have circular cross sections along a certain axis. That is to say, when you cut such objects perpendicular to a certain axis you'll get circles. Examples of such objects includes rods, poles, wineglasses, and pails. A Blender render at the left shows some of these.
With the Spin tool you only have to "model" half the outline of your object. The object is completed after you spin this outline. A bit of cleanup here and there and your model is finished.