If you have ever asked what is the difference between Any CPU, x86 and x64 options in Configuration Manager platform, the answers can be very scarce and scattered through all the Internet.
However, Sayed Ibrahim, a fellow VSTS MVP has gathered in one all the responses he had so far. Check out his MSBuild: Building 64 bit versus 32 bit. Do not get misled that the post is only MSBuild related. Same principles apply for all CLR applications.