Aperture: working on images that aren't accessible

This one blog post convinced me of the value of managing images outside of Aperture:

Editing Offline Images - O'Reilly Digital Media Blog

... The best part of this strategy is that you can still do quite a bit of work on your images even when your large external drives aren’t hooked up. You can’t make image adjustments to your photographs, but you can keyword and rate. This means you can edit your shoots down to your selects without the master images being available. And, you can also figure out which images should be rejected and deleted out of your image library forever...

This is a huge advantage for me. I can work on metadata from a laptop without the fear of losing a massive image library.