Take a look at this page from the Tomcat documentation:
It references your question. Here is the paragraph that I believe provides insight to your comment.
Copy the web application archive file into directory $CATALINA_HOME/webapps/. When Tomcat is started, it will automatically expand the web application archive file into its unpacked form, and execute the application that way. This approach would typically be used to install an additional application, provided by a third party vendor or by your internal development staff, into an existing Tomcat installation. NOTE - If you use this approach, and wish to update your application later, you must both replace the web application archive file AND delete the expanded directory that Tomcat created, and then restart Tomcat, in order to reflect your changes.