The most significant thing about the speaker is the fact that he's dead. He tells us the tale of his own death. It is also important to think about how he tells us the story. He doesn't seem too worked up about it—quite the opposite, really. He tells us part of the story in a fairly dry, matter-of-fact way, and he tells us other parts in a kind of mysterious, figurative way.
So, what are the advantages of having a dead speaker? It gives the poem a very different tone than it might have if the speaker were recounting the death of a friend or fellow soldier. It is unusual for us to be able to discuss something as dramatic and emotional as a violent death in such a detached or metaphorical way as our speaker does.
Imagine you had witnessed a very emotional, dramatic scene like the one in "The Death of the Ball Turret Gunner," and then imagine yourself telling your friends about it: "We were, like, flying along and then all of a sudden there were all these planes and I was like WHOA! It was totally intense…" A survivor's story, even if it is about the death around them, is also at some level about their own survival. By writing this poem in the voice of a dead soldier, Jarrell is able to make every aspect of the poem contain the element of death, even the parts that are about living.
The living are always going to have a very different perspective on death than the dead. Just ask a zombie. Okay, bad example. You're right, zombies are technically undead, Shmoop was just testing you to see if you were still awake.