When his money is his money and her money is hers

When my husband and I first met we were both grad students, just making enough money. However my husband had a significant amount of credit card and student loan debt and I had zero of both. However, since the very beginning it was always all of our money. We lived together before we got married and we always counted our incomes as one household income. So, it was just easier once we got married to get a joint account and have our paychecks direct deposited there. At first we still had his and her checking accounts but we never really used them, so we decided to cancel them and let it just be the joint account.
However, I also have seen a different experience: one of my close friends, who also lived with her husband before they got married actually splits the household bills, everything! She keeps her own checking account and he keeps his own and when the bills come they split them fairly, I guess. This seemed to work for them, in particular because he had a significant amount of credit card debt that he was paying down on his own with the help of a second job, and she didn’t think it was her responsibility to help him out.
I always wondered, when you have found the person you think you will spend the rest of your life with, don’t you feel like his/her struggles become your own as well? Instead of going in with the attitude of: you got in this mess get yourself out of it?
Married or unmarried, if you are with your long-term partner how much are you involved in each other’s finances? With my friend’s case, it just always seemed to me that because they had divided finances, that didn’t give much of on opportunity for actually discussing how each was doing financially. What if the other person was actually struggling, or incurring debt in order to pay her share of the bills? Whereas with a joint account, the truth is right there in front of you, you know as a couple the type of life you can afford to live.
But even with joint accounts, it seems like there’s always one partner who takes charge of the finances while the other can’t be bothered with it. How involved is your partner in your household money management?