- For adding some specialization and recognition of content for
different archived files just like file  extentions *.jpg *.bat *.sh *.html
even though *.bat is essentially a text file ...

- Put some limitations/features for specific uses e.g. we expect .war to
be a web archive so it would have WEB-INF subdirectory. Also we don't
expect to have EJB Container stuff in .war. These give hints to deployer
(server)application on what Deployment Descriptor to look for.

there are some other delicacies as well.