I was told I was financially controlling/ borderline abusive to think that people should have a set amount of pocket money once the bills are paid
I suppose the deciding factors are based on whether people are spenders or savers.
If neither people overspend, as in they naturally spend less than the household income, either because they don't buy very much, or because income is high, the 'one joint pot, we just both spend from it how we like' model can work and be fair.
However, some people, faced with a joint account containing thousands of pounds, would be imagining buying cars, holidays, expensive work lunches, gadgets, clothes when they already have some, hobby equipment etc etc.
Which is no good if that money needs to pay the mortgage, childcare, bills, food etc etc.
So it can help if adult personal spending money is separated out, so joint essential costs are covered and both parties have some money of their own.
It's also important to recognise how frequent small purchases can really add up over time and skew a budget that doesn't have a lot of spare money.
For example, people might wonder why they never have any money and can't afford a holiday or decent car etc, but if they're the type who buys a coffee on the way to work and their lunch in Pret or similar each day, that could be £50 a week, £200 a month so over £2k pa which is really significant unless you have a decent amount of spare money, so as well as discussing large one off purchases, there often needs to be discussion and agreement about this sort of spending.
Because if not, you could have one partner worrying about covering the basics and the other merrily buying themselves small treats daily. Now of course eating and drinking during the working day is essential, but the cost has to be affordable and fair within the family.