I read this article at Salon about how families are going into bankruptcy not because they are spending way to much money on lattes, but because they are counting too much on the double income from both father and mother. In the past, when moms usually stayed at home, there was only one income to count on, when dad lost his job, mom could go out and work while dad looked for another job. This lessened the financial impact on the household.
Now that a lot of families have two incomes and rely on the entire amount for their financial well-being, if either of the parents lose their job, they are more at risk for bankruptcy. This is because their higher income has come to mean higher fixed costs such as mortgages, loans, insurance, medical, education which are harder to maintain if one partner loses a job. Whereas, when only one parent worked, both parents could go out and make up for the difference in income.
I guess what I understand is, just because you are getting married, you should not use the combined incomes as a basis for your budget because it makes your family more prone to risks.