Its important regardless if you run an aftermarket system or not in my opinion.The big 3 helps the alt from working as hard(running harder to charge the batt,and keeping your voltage up when you draw more than stock supply than the vehicle is currently needing).That alt is already working its azz off already just keeping up with the stock supply and demand.Car manufact. place/do the bare min that they can get by with, and the cheapest.Ever run down the road and decide its pretty hot outside at night and turn on the a/c and experience that jolt/down draw with the lights dimming?Thats the struggle/amp draw thats wearing out the alt,and batt isnt keeping up with the demand,thus working/wearing out the alt do to the ****** electrical supply that they get by with,costing you more money in the future to buy alts a batts sooner than you really need.I mean, $50 bucks to do the big3 verses buying another alt and batt sooner than need be and spend $130+ on an alt and $120+ on a batt? No brainer there.As for the amps..They need 14.4v to get the max potential that they need to perform at theyre best,but low voltage constantly will ruin/fry an amplifier do to poor supply and demand.Most amps these days will do fine in the lower 12v range,but never see the actual performance that they can produce given the upper voltage,yielding in less performance/output,and those wanting more and experiencing less than expected.Dimming lights when you are playing a system is an indication of poor supply/not enough power for the demand which will ruin/damage an amplifier/amplifiers,along with components within.Im not an electrical engineer, but I have experienced failures(money loss,and equiptment loss) due to poor voltage issues,and have experienced what the big 3 has done to maintain my voltage,and keeping up with my supply and demand needs for as little as it cost.I recommend the Big3 on any vehicle whether it be adding an after market audio system or not if you want your alt and batt to last longer.If you experience dimming lighting..do the big three,and run what you have