In my opinion, when specing out high-powered systems, people don't factor in the vehicle's ability to provide enough power to push the equipment. Typically trucks have higher amperage alternators, which helps, but its not always enough to push a 1000+ watt system.

When I used to run my system without a cap, the quality of the speakers would degrade the longer the system was in use. Since I've been running a cap, years, I have not had that problem with that. Sustained quality and harder hits. So while a capacitor is a smaller (bandaid) solution to upgrading the charging system, it does provide some benefit.