Been asked this quite a few times when I've shown my classes some rigs. Seems easier to do a quick vid and point people here. (this is another one that's been sitting on my computer for months that I forgot to post)
I usually put my rigs under multiple levels of master controls (both for chars and props) and the main reason is that it seems easier to me to default to doing that, than to have to go back and add more controls when an animator wants to do something crazy like add something to a motion path and still retain some type of control. I mention a few other circumstances where this is useful, but to be honest, it just seems like common sense to me and makes me grumpy.
So get off my lawn.
Maya/Rigging: Using multiple Master Controls from zeth willie on Vimeo.