preloadEnable y startMode: https://blogs.msdn.microsoft.com/vijaysk/2012/10/11/iis-8-whats-new-website-settings/
Application Initialization <applicationInitialization>: https://www.iis.net/configreference/system.webserver/applicationinitialization
IIS 8 What’s new – Website https://blogs.msdn.microsoft.com/vijaysk/2012/10/11/iis-8-whats-new-website-settings/
When you set the startMode property of your application pool to AlwaysRunning a worker process is spawned as soon as IIS starts up and does not wait for the first user request. But this does not mean the web application is initialized.
When you set preloadEnabled to true, IIS will simulate a user request to the default page (can be changed with initializationPagemetabase setting) of the website/virdir so that the application initializes. The request is not logged in the IIS logs.