It all depends on what you will be using it for. Your basic line driver is only going to increase the pre amp voltage into your amp (Anywhere from 5 volts up to 13volts) wich will allow for a cleaner signal coming into your amp. This allows you to keep the gains on your amp low wich helps reduce hissing, pop, crackling, and feedback that you can hear in your system. Now the real benifit of using a line drier in compitition is when you are running multiply amps. Your typical headunit is going to have pre out voltage ranging form 2 volts to 4 volts. If you are running multiply sub amps what happens is as with each amp you run the pass through into another amps rca input and so on that voltage level will reduce with reach amp that it passes through. This instills you losing s/n ration on the amps, with in tern will cause some amps to be stronger than others. YOu would have to do alot go gain matching inorder to make sure your amps are all outputing the same. This some a big issue when you are running multi amps to a single sub. You don't want one amp to be stronger than another because it will over load which ever coil the stong amp is on and in turn cause the sub to fail over time. Now with line drivers supporting multi amp out puts such as AudioControls Matrix and Maxxsonics MaxLink. These units do more than just step up the pre amp voltage. These units allow to you run anywhere from 6 to 10 amps at one time (The number that was given is with straped amps) This allows every amp at retain the same input voltage. These units also allow you go gain sertain frequencies ranges.