thats the benefit of it.i think an isolator helps if your going to play it with your car off.
Benefit being you can't run down your starting battery if you play it too long with the car off.thats the benefit of it.
otherwise running it parallel is the way to go.
When you don't want to bother the neighbors with the sound of your motor running... //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gifyeah but that goes against common sense in my mind dave.
if you are going to have a moderately powered system or higher... unless your burping... why would you beat music with your vehicle off?