I don't have time to delve into it, but basically think about how much excess carbon particulate your engine generates and how little of it actually gets out of the engine. That stuff has the potential to clog up stuff inside your engine. The first time I ever cleaned them out was just recently, at 160k...barely any carbon came out of the exhausts, but the idle is noticeable smoother. Either way, it can't hurt to do it...grab a bottle of seafoam and slowly suck 1/3 of a bottle into your engine through a vacuum line (PCV or brake booster work).