Actually, they benefit active duty military families AND retirees.
Frankly, I am not a fan of commissaries. One can find better products for the same price off base. But there are some bases that don't have a grocery store nearby.....
I keep a very close eye on my family's grocery spending. The commissary is indeed much cheaper. We routinely save well over $100/mo on commissary shopping vs. chain store shopping. And, since commissaries have the same products as any normal grocery store, I'm not sure how you can "find better products."
Fort Irwin, CA...35 miles to civilization and I mean civilization, but right next to Death Valley.