The main reason to restart your server is to update the environment varaibles. A restart might not be necessary, but it is one way to be sure the environment is refreshed properly upon install. Restarting your IIS services could well be enough. When you do it be sure that the Path variable from under the Environment section of the output of your phpinfo.php file contains the correct environment variables.
The main reason to restart
The main reason to restart your server is to update the environment varaibles. A restart might not be necessary, but it is one way to be sure the environment is refreshed properly upon install. Restarting your IIS services could well be enough. When you do it be sure that the Path variable from under the Environment section of the output of your phpinfo.php file contains the correct environment variables.