I don't think it is a matter of setting rules for how every couple should run their finances.
We are all different and the couple needs to discuss between themselves how they are both happy with things working.
It is good for each to have 'their own' money that they can choose how to spend, as well as both contribute toward the bills and responsibilities of the home and family. It is not a good iudea for one to be carrying all the bills and the other have all their money to spend how they want to.
A joint account might be an idea that they can both contribute some money in to each month from their own personal accounts. And then from the joint account have an agreement how the money is spent (bills, groceries etc). However it is not essential to have a joint account for this, simple one of the possible ways to do it.
If one person in the couple is good with money and the other terrible with handling cash, then it also may determine how they run their finances. If they have a joint account and one is placing money in there for bills and the other is taking it and going to spend it on luxuries for themselves because they cannot resist sales in the shops, then it may be better to not have that joint account.
As I said, it is not a matter of 'this is how it has to be done', but rather a matter of the couple reviewing how good each is with finances, knowing their weaknesses with money etc and deciding between themselves if a joint account is a good idea