Alright, here's a example. It's just one of many.
You have a list of user names and various tokenized information about them stored in a hash table.
You have a nested looping function which is going line by line through, lets say, a log file... and for each line, it has to loop through (or query) various users from the hash table. Lets say this script example is auditing the users based on Joins and Parts to a channel log. For each Join the first loop hits, it either adds the user to the list, or maintains their existing tokens if already in the list. For each Part, it slates the user to be removed (-u0) if they don't Join again later on in the log. At the end of the log, all users that have been slated for removal fall off the list, while all users who had Joined again lost the -u0 flag in the subsequent hadd.
The above example CAN be done in other ways, but this example is suppose to unlock your mind to the potential of some methods out there that can benifit from this. Be it an existing script that is being converted from Variables to Hash Table, or a new script with an entirely unique and valid use for -u0 flagging.