An application pool is a configurable entity that allows you to control how IIS maps IISWeb sites and virtual directories to instances of the IIS worker process.The routing architecture of IIS is controlled by a kernel-level device driver named http.sys.This listens to the HTTP requests and uses the information in IIS Metabase and routes the requests to the instance of W3WP.exe is associated application pool.
If http.sys determines that the target application pool doesn’t have a running instance of
w3wp.exe, it launches a new instance. When http.sys launches a new instance of w3wp.exe for a specific application pool,it uses the application pool identity to initialize a Windows security token that serves as the process token.
If we want to refresh the XML file as part of feature refresh, instead of IISRESET, Application pool restarting might help in saving some time.The main advantage of using this technique is that it is faster than a full IISRESET command, which restarts all processes associated with IIS. Using this command instead of an IISRESET command can save you a few seconds here and there.