In my website's application pool, the identity is set to "ApplicationPoolIdentity". Normally I would use "Network Service" and give read/modify rights to "Network Service" on the website file system. However, someone told me to use "ApplicationPoolIdentity" instead because the site will have their self contained permissions (so one site cannot update files of another when all under "Network Service").
What NTFS user should I use for providing read/modify permissions to a website's "ApplicationPoolIdentity" though?