I refused to have a joint account with my ex wife because of her insanely bad spending habits, I was already having to give her money on a regular basis because she would spend money on stuff she couldn't afford all the time. I paid 3/4 of the bills she paid the rest, which was minimal, she had more money to spend than I did most of the time, yet complained she didn't to. I saved for things I wanted, she just spaffed it on trash. She never really paid for anything like takeaways, nights out etc. Didn't spend a penny on our house for work that needed doing, ever. Always expected etc. Her dad always bailed her out before. He has just got her out of 10k debt when we met.
I Finally gave in. Within a month, noticed money coming out of the joint account. Kept on questioning her and she said she'd put it back if she took it out. She did very occasionally put it back, but most of the time didn't.
I'm also still giving her money at this point. Then noticed the account started going overdrawn. She had put an overdraft on it...
Eventually we broke up for many other reasons.
Current partner, we are buying a house together at the moment. I earn over double what she earns. She is not interested at all in having a joint account. My money is mine, hers is hers. She pays her way, she pays for days out, she pays for take aways, she buys what she wants without getting herself Into debt. She's happy for the bills to come out of my account. She pays for things for the house, which is currently just mine as I bought it after divorce. She very rarely will let me help her out or buy her something she needs! She is very independent.
It works best for us this way. While I still am a bit weary of joint accounts, I wouldn't be against having one that we just used for bills, as she is far more sensible.
Edit - just to say, I had no kids with my ex as I never wanted them, and neither does my current partner. So that probably makes a difference in our situations, compared to others.