If you have multiple users using your Engine computers, and you want to have the Engine disabled when a user logs onto the machine and enabled when they log off (for example, to use idle machines in a computer lab for rendering when no user is actually logged in), this option will speed up the operation of a log-off script to enable the Engine.
The log-off process normally has to wait for any scripts or processes run at log-off time to finish. The Engine Shell component application waits for notification from the Master that the command has been sent. Because this can take some time (for example, if the Master is busy), you can use this option to speed things up. This option adds another Service that runs in the background on the local machine. This service acts as an intermediary between the Engine Shell component application and the Master. The Engine Shell will send the request to the Service, which then will forward it to the Master. This makes the whole process much faster, because the Engine Shell only has to send this one request to a process running on the local machine, and can then terminate itself, allowing the log-off process to continue.
See the FAQ How can I control the local Engine from a commandline?