I'll again echo beatledog's excellent post.
Even the most trusting and loving of couples can sometimes not see eye to eye on the perceived value of a purchase. Any purchase, small or large.
Having 3 bank accounts takes away us questioning each other over the value of acceptable purchases that are really minor in cost, and focuses the attention on the larger, family unit ones. We can and do still fight over those, and that's where the fight should be. It keeps us from fighting over how I just spent $100.00 on 1,000 bullets, or she just spent $100.00 on a pair of shoes.