Remote Assistance and Remote Desktop are different features of Windows 7 that have entirely different uses.
Remote Desktop is based on Microsoft Terminal Services and is a tool for remotely logging on to remote computers.
When you use Remote Desktop to connect to a remote computer, a new user session is established. Remote Desktop can also establish sessions with computers that have no interactive sessions running (no users logged on locally), such as headless servers.
For more information on Remote Desktop, see Chapter 28, ?Connecting Remote Users and Networks. Remote Assistance, on the other hand, is a tool for interactively helping users troubleshoot problems with their computers. To use Remote Assistance, both the User (also called the Novice) and the Helper must be present on their computers.
Unlike Remote Desktop, Remote Assistance does not create a new session. Instead, Remote Assistance allows the Helper to work in the existing session of the User. The User’s desktop gets remoted to the Helper, who can then view the User’s desktop and, with the User’s consent, share control of the desktop.
Here is another way to summarize the difference between these two features: In Remote Assistance, both users involved are looking at the same desktop using the same logon credentials (those of the interactively logged-on User) and can share control of that desktop; in Remote Desktop, when the remote person logs on, the interactively logged-on user (if one exists) is logged out.