How do iso. cones work and what are the benefits?

I know this is kind of a newbie question, but what exactly is the idea behind using brass isolation cones under a cdp? I went to try to explain the purchase to the wife, and then realized I didn't exactly know myself! They seem to be very popular, but I am unclear on exactly how they work or what the benefits are.
Is the idea to "drain" any internal vibration from the cdp?
Are they equally as effective under other components such as and amp or pre?
Also, I would appreciate any advice on their use, any tips, placement, etc. Thanks, Jb3