Virtual Hard Disk or VHD acts like a normal hard drive built into your computer. Cool thing is, it comes in a form of a single file so you can make a copy of it and virtually attach it to any other Windows computer.
If on your Windows 7 computer opening programs, saving documents, browsing the Internet and other every day tasks are getting slower, this is how you speed up things without installing an additional program.
If you are tired of waiting for your Windows 7 computer to shutdown or restart, you can create a new shortcut that will speed up the process considerably.
You have more people using one computer and you don't want them to be able to shut it down using a shutdown button on Windows logon screen, this is how you remove it.
In this day of age, it's very practical to have a Windows 7 installation on your USB key, for many netbooks and devices don't come with CD/DVD drives anymore.