Sometimes with Network secure PCs and high end workstations, all it takes is for certain root accounts to have their account passwords changed locally, or to have a group removed and a perfectly good install with useful data winds up being shut out from admins; so, you have to either use a boot CD , or a USB boot to clear the account, then reinstall the password or passphrase, and the group, then the PC can be repaired ( its also useful if the Motherboard dies and the access is linked to biometric passwords, or there are groups also deleted). The disks that most admins use are pretty useful, and obviously it pre-supposes a level of trust with its use. However, the CD and now the USB boot can now run all sorts of utilities that can help save an install, and even rescue data before the disc is replaced or re-formatted. There is a positive use for the USB boot , and the CD boot which can make key changes, but if you log access at this level, then it seems to track any issues. But hackers to always find a way if it is not locked down well, but all it takes is one bad admin to mistype or delete a group, and the PC is in a state that needs a rescue. I have seen encrypted laptops that have been rescued by Boot USB and CDs to get key Project data that was never backed up. It's an essential set of tools to rescue PCs and the data therein, IMO.