Why Have Cryptography
If the confidentiality or accuracy of your information is of any value at all, it should be protected to an appropriate level.
If the unauthorised disclosure or alteration of the information could result in any negative impact, it should be secured.
These are simple and widely accepted facts. However, the means to achieve the requisite protection are usually far from obvious.
A number of mechanisms are commonly employed:
Controlling access to the computer system or media. For instance, through 'logon' authentication (eg: via passwords).
Employing an access control mechanism (such as profiling)
Restricting physical access (eg: keeping media locked away or preventing access to the computer itself).
A MORE FUNDAMENTAL APPROACH
All these approaches can be valuable and effective, but equally all can have serious shortcomings. A more fundamental approach to data security is cryptography.
Conventional access control mechanisms can often be bypassed (for instance via hacking). In addition, what if data has to be transmitted, or if the data media (eg: floppy disk) has to be moved outside the secure environment? What if a number of people are sharing the computer environment?
Cryptography (encryption and decryption) is a technique designed to protect your information in ALL such situations.