You could type that notice over and over again. Or, you could use an entity to call it forth in place. Entities can reduce errors . By the 101st time you type that copyright notice, it is likely your poor fingers will be so tired you'll make an error and set your copyright for 1989 instead of 1999. Using an entity can reduce the potential for these types of errors.
Entities are easy to update.
Without an entity you'd be searching and replacing throughout your document set. Entities can act as placeholders for TBD information. Maybe legal hasn't quite finalized what they want that copyright notice to say. You can get quite creative with the use of entities, and even have documents that are constructed entirely from entities. One approach you could take is creating 10 or 12 separate flat files, with the appropriate biography information into each.