Why do they make them? People buy them.TECH TIP:
Does your bass sound washed out? Do your headlights dim when your subwoofers kick in? Chances are your amplifier is using more power to drive your subwoofers than your electrical system can supply. We recommend the use of a stiffening capacitor (above) for big bass applications. A stiffening capacitor runs in parallel with your amp and acts as a reserve power source. When your amplifier needs that extra current for big bass output, it can draw extra power from the capacitor without putting strain on your already drained electrical system.
Why do people buy them? Lack of education/knowledge? Etc, of course.
Just a little advertisement I came across. No big deal. Just this is what they're advertising. No intention of this becoming a flame war. First post that way means it's gone.