We have joint account, and as I'm a sahm at the moment, his is the only income. Though all our savings are "mine" (as in i brought them to the marriage, so now ours).
We are both careful with money, but our main area of disagreement is over "recklessness". Oh, and what constitutes good value...
I find he "wastes" money by not making his mind up soon enough. Like missing out on early rail fares because he's either forgotten to book, or still thinking about what time he wants to leave etc... i consider it wasteful because by being more organised he could save money. Or things like buying something, but being charged the wrong amount (like buying a £5 book on offer, but it not going through at the till and he pays £8), then when he realises it, he can't be bothered to go back and point out the error, so he ends up paying more.
But he thinks I'm wasteful because is rather pay more for something better quality, when he thinks the cheaper version will be fine. And sometimes he's right, the cheaper version is fine. And sometimes we end up paying more to buy 3x the cheap one as it keeps breaking, rather than just paying once for the better one.
We don't argue about it, as such, but i do get a bit frustrated and eye-rolly, when he's once again missed a deal by being essentially lazy...