This feature allows users to install Microsoft’s Virtual PC application and then install and run a complete fully licensed version of Windows XP SP3 from within the virtual PC environment. This feature was originally developed for businesses to migrate from Windows XP to Windows 7, and give them an environment from which to continue using any older non–Windows 7 compatible software. It is not suitable for applications which require 3D graphics or hardware accelerated sound, so gaming or even using your old TV tuner to watch TV are definite no-nos
As you can see from these explanations, the additional features present in the Professional Edition of Windows 7 are focused more on a business style or corporate workplace environment, and are not generally necessary for the average home PC user.