In my personal opinion its a bad idea.
You are seperating your finances under the illusion that somehow your problems financially will go away. They wont. Behavior has to change in oder for the circumstances of the problem to change.
For the first half of our marriage, we had quasi-seperate finances (two joint accounts, so that debit cards didn't cause issues), and seperate credit cards. Later, when I got involved in an LLC/partnership for business reasons, we completely seperated things (so that nothing could come back on him if the business went bad). We are both on the mortgage, but that's it. He pays the household bills, I direct deposit money into his household account. We both still consider it "our" money, we consult on purchases etc, and pass money back and forth freely, but I like knowing that if one of us has a legal issue, everything we own won't get frozen.
We have been living together for 4 years now, and she has her own savings/checking/credit cards and I have my own. We have nothing that is joint (at least yet) and we like it that way. I pay for all bills one month, she pays for everything the other month. We can see how much money we make, how much we can save each month and what we can afford. It gives us a sense of pride and accomplishment to see our own progress and how we handle money.
I really don't think it matters how you budget and how you keep track of spending and who pays for what. At the end of the day it all comes down to your spending habits, if you like to spend money you will spend money and will find a way to spend it (even if you don’t have it).
We always discuss bigger purchases either for the home, or personal use. We don't have a set amount when we starting talking to each other about a purchase. We are not asking each other for permission, we are more discussing it so we know what we are buying and if it makes sense, should we wait with the purchase or not, do we really need it or will it sit in the corner and collect dust. Me telling her what I would like to buy is for me to see if I really need it as she always gives me her opinion. I trust her and she trusts me that we will not go crazy and spend all of our savings on useless items. I guess I am pretty lucky to have found someone that is responsible with money.
I don't mind keep the financial assets separate. It is a great solution essential to prevent any possible and annoying clashes over the distinct differences in spending styles, for instance.