what is hashing algorithm

What are 5 benefits of using a Hash Algorithm?
Doing a powerslide project for a internet security class. Been everywhere looking for 5 pros to using a hash algorithm.even my book, but could not find any.
Links or tidbits of info for each 5 would be greatly appreciated.
1) Unlimted size of the storage
2) Fast access of the required entities
3) Key based retrieval, easing the accessibility
4) Possibility of individual hash function for each entry
5) Ease in maintaining unique reference entries
General info
http://en.wikipedia.org/wiki/Hash_function
List of different algorithms
http://www.securitytechnet.com/crypto/algorithm/hash.html
Creating one such algorithm
http://www.azillionmonkeys.com/qed/hash.html
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