I found this quite interesting. Make sure you check the original source http://www.hanselman.com/blog/TheMagicOfUsingAsynchronousMethodsInASPNET45PlusAnImportantGotcha.aspx
First, I encourage you to listen to episode 327 of the Hanselminutes podcast. We called it “Everything .NET programmers know about Asynchronous Programming is wrong” and I learned a lot. I promise you will too.