the line lock goes into the front brake system, upon activation, it locks up the front brakes.
when you depress the brake pedal, and hold it to the floor, the activate the line lock, it activates a solonoid that closes off and holds pressure on the front brakes only,
this way in the burnout box you can activate the line lock, hold it, and do your burnout without risking taking out the rear axle or wearing out the brakes.
also on the line, you can activate the line lock and that way you dont have to put pressure on the brake pedal and have the front and rears applied at launch, you can stall up a little more, keep more concentration, and actually get a better 60ft as all you are releasing is the front brakes