I think everyone covered it from the Blender world, but I wanted to point out that in other 3D software their are differences between the types(DEF, Control, and MCH). Like in Maya the control is actually a curve object(usually). Animation master 2009 the MCH bones are a different object attached to the deformers(DEF bones in Blender). So learning to have it as separate pieces will also help you if you ever have to work with other 3D rigging software.
