Nobody can really prove that having a closer is the best way, but it's the traditional way, and it's safer for the manager to have one. The media can much more easily understand the narrative of sticking with your closer (Lidge, Giles, Neris) until you don't, and then you get another closer. When it doesn't work, it's the closer's fault. When you have no closer and it doesn't work, it's the manager's fault. And when you lose a low-scoring game because Tommy Hunter gives up a run in the 8th inning the articles will also talk about the offense, but if the closer does it in the ninth, that's what the story is about..
Much as the first week disaster reset Kapler's approach it seems Neris being sent down and the ensuing chaos, win or lose, is going to end with Seranthony closing, though I hope it's not exclusively the case (i.e.having him face the most important batters has been working).