basically instead of using the gain on your amp you can use the little remote adjustment for when you are at say a comp and want to burp your stuff at full blast.
turns the amp on when the car is on or in the 'ACC' mode. you'll need to run that from the remote turn on lead comming from your head unit. should possibly be a blue wire but sometimes its not. the wiring diagram should be in the maunal for the HU.