Let's keep the math simple, and say that you make 10,000 a year.
If you're single, you'll be paying 2% of your income, solely for California state tax, that's $200. But, then you decide to get married, and your partner wants to stay home with the children, as usually the reason to be in a marriage, and you still only earn $10,000, you will only be taxed at 1%, which will be only $100.
These are paystubs for couples, tax rates differ in a few ways, state to state, level to level of income and also couple or single. This pages shows the different tax rates for couples