1. Security Context – In ASPNET Development Server, it is determined by who you login as on your computer. In IIS, it is typically IUSR_MachineName.
2. Accessing Static Pages – In ASPNET Development Server, you can not access static pages in a secure folder if you are not logged in, but in IIS, you can.
For more info, please watch the 7-minute video below or refer to the excellent article: Core Differences Between IIS and ASPNET Development Server