How can you strong sign an assembly using key located in key container (not in a file) from within Visual Studio 2005 (SP1)? You can’t. For whatever reason MS decided not to give us this option in the 2005 RTM timeframe (apparently they didn’t have time). Now, much later, they apparently still don’t have enough time to implement it.
Why would one bother? Because storing strong key in key container (which is protected by OS) is more secure. It is also easier to reference such strong key as you need only its name and not the entire file path.
At least there has been a workaround which still works.