One team, one pot...why split
That only works if neither party is a spender, or if they have plenty of money to cover all their essential expenditure and everything else that either of them may ever buy.
Many people do not, so just spending everything from one pot could lead to a situation where they can't afford an essential expense because one of them bought an expensive personal item without thinking about whether they could afford it, or if one of them is always scratching around for money for clothes or other personal expenses while the other spends a fortune each month on discretionary expenses like coffee, lunch and drinks out, clothes and personal grooming, gadgets, etc etc.
So it's good to separate essential and discretionary expenses, also good to plan for expenses that will occur in a few months time, not just thinking 'there's money in the bank now, I can spend it if I want to' and it's also good for them to both have the same amount of spending money, why wouldn't they?
OP, if you're new to money/budgeting etc, a good place to look would be the Moneysavingexpert money makeover.
Have a read and do whatever is relevant to you, even if you have plenty of money at the moment, most people can still benefit from cutting their essential bills, which leaves more money for more fun stuff and will also enable you to save for the future, which if you're getting married soon, there's a reasonable chance that might mean children within the short to medium term, with the associated loss of income and/or increased costs so if you have a head start with saving to cover these costs, things will be a lot easier.