You know, I overstated my own position. A couple people have pointed out that it depends on the event how much a backstory matters. It also depends on what you do with your backstory. In one of the units I belong to, we have regular mail calls. In order to make those letters meaningful, a number of us have circulated short bios of our on-field personae. This technique really works to make mail call a powerful first-person experience.
I use my backstory to create a period presence that is easy for me to remember, too. For instance, I'm an old armored tanker in real life (a DAT if you will ) I still pay attention to some of those armored/cavalry issues. So in my younger days, I was a cavalryman, though I am not now. I've also traveled a lot in and studied the history of Panama, so I went to California by way of the Isthmus. Quite and adventure, let me tell you...
How I ended up in Wisconsin in 1861? Well, now youngster, that's another story.
Mrs L: You weren't cooking doormice, were you? The Emperor has declared that to be illegal, though I can't see why. I've heard hey're good stuffed.
Pine River Boys, Co I, 7th Wisconsin
"We're... Christians, what read the Bible and foller what it says about lovin' your enemies and carin' for them what despitefully use you -- that is, after you've downed 'em good and hard."
-Si Klegg and His Pard Shorty