If you've got more than one Department or Subsidiary in your Organisation, it is obviously useful if you can separate the relationships for say, the Sales and Purchasing Departments.  Similary it can be useful to separate your Wife's friends from your own.  It can also be useful if you are trying to find someone in your database:

Suppose you can’t remember someone’s name but you can remember that they are someone else’s sister.  In a conventional system you would not be able to find them - particularly if they were married.  In GEM you can.

Again, suppose you can’t remember the name of a subsidiary company you want to find.  In most systems you would be sunk.  GEM automatically creates Organisational structures for you when you input an Organisation's parent Organisation.  This enables you to simply display the organization structure for the organization whose name you can remember, and it will show you names of all the organisations in the group and their staff.

So often it's the relationship that we can remember, not the name - a Supplier's Solicitor, or a Customer's Advertising Agency for example.  Often you wonder why someone is in your database.  If you know their relationship to someone else, the answer it often self-evident.