If you are into PC repair and are faced with doing some work on a Mac, having a software tool like AppleJack could very well prove EXTREMELY useful. Certainly best suited for advanced Mac users, those who do PC repair ought to be okay with this tool especially if they are used to working with scripts or with Unix/Linux type environments.
Whether you are looking to work around the fact that you do not have a startup disk to help you to work with a problem booting, need help removing a problem swap file or just want to clean up your cache, AppleJack is where it is at.
I would again stress however, this is not for the kiddies and is best left to those who understand the underlying inner workings of their Mac. If you do not, I would suggest passing this otherwise great tool over for those who are more familiar with this kind of tool.