Most application servers/JSP engines can load JSP servlets dynamically. This allows the application server/JSP engine to load the JSP servlets every time you configure them.
For example, suppose you configure your auto-reload time for one second. The JSP engine will load that JSP servlet after every second. Though this feature reduces development time by avoiding the restart of the server after every change in JSP, it results in poor performance in production because of unnecessary loading and burden on class loader. This is why disabling the auto-reloading feature in your configuration improves performance.