As you all know, the purpose of bleeding brakes is to remove air from the brake system. When you install a new or rebuilt MC, what is it full of? You guessed it, air. Rather than distribute all that air throughout the entire brake system, and then try to chase it out all the bleeder screws, you can "bench bleed" your MC and eliminate all that air instead of introducing it to the brake system. I know what you mean Fumblin', bench bleeding, floor bleeding, kitchen sink bleeding, not quite the same, but none the less, I know what you mean.
On a dry system you still have a lot of bleeding to do, but at least you have a place to start. I've replaced MC's on a full brake system, and haven't had to do any bleeding of the vehicle, simply because I "bench bled" the MC.
Hope this helps explain it a little bit.
