I use the banking mod and although the question who owns how much money doesn't come up often, WHEN it comes up, that mod is critical.
Currently I have sims from different households merged into three teams for a challenge, and one of them receives royalties. It would be a hassle to deduct these manually from the challenge household's funds every day and later add to her original household.
Also many servos in my game have to buy themselves free, so I set up bank accounts for them.
And finally on a more everyday note, a kid or teen saving up to gift their parent something for an anniversery or birthday also needs to keep track of the extra money, even if in normal gameplay that same kid can draw from the household funds normally.
Another thing are college funds. Savely tucked away on the bank there is no temptation to use that money for a new couch.
Long story short, I think a banking system would be better than tracking individual funds, because it will be there when the player needs it and otherwise sit silently in the background. That way everyone can customize how complex they want their game to be.
