One of us likes to impulse buy cheaper things, the other likes to save up and buy more expensive things.

Having a joint account + individual accounts helps take away the stress that having differing spending habits has on a marriage.

Protip: If you feel like having individual accounts sets up the field for "cheating" you can have multiple "joint" accounts at the same bank. Keep a real "joint" account, and have 2 additional "joint" accounts you treat as individual accounts.