An Application Pool can contain one or more applications and allows us
to configure a level of isolation between different Web applications.
For example, if you want to isolate all the Web applications running
in the same computer, you can do this by creating a separate
application pool for every Web application and placing them in their
corresponding application pool. Because each application pool runs in
its own worker process, errors in one application pool will not affect
the applications running in other application pools. Deploying
applications in application pools is a primary advantage of running
IIS 6.0 in worker process isolation mode because you can customize the
application pools to achieve the degree of application isolation that
you need.