We didn't have a pre nup. Thought I didn't need one.
Post nup covers things that a mean WS would fight about in an ugly D. Our state doesn't care about A's, so they would split all assets and debts 50/50.
My post nup will make sure finances aren't split 50/50, but go more in my favor, since I gave up my career to homeschool our children on the promise of fidelity and an intact M until the day one of us died.
It protects my (small) inheritance, and the house we bought using part of it (after A.) Our state would make us sell the house and split it 50/50. Post nup says the house is 100% mine, not his. I would have to sell it if we D, since I couldn't keep up the payments, but wouldn't have to split the equity with him.
It also lists jointly approved credit cards. (Credit cards are no longer jointly owned, however.) It says those credit cards listed, with balances up to $X,000, are split 50/50, anything above is the card's owner's responsibility. Any cards or debts not referenced in the post nup are solely the responsibility of the person whose name is on it. This is because people in an A mentality can rack up debt to support the A.
I don't have my post nup finalized, because we can't afford the legal fee right now. WH suggested I pay for it with part of my inheritance. I shouldn't have ever needed it, and I'm not going to use my inheritance to set it up.
Everyone's case is different. You can sometimes find a lawyer who will discuss it with you for free. In my case I had to pay $100 for the initial consultation. He wants $2,000-$3,000 to finalize it...
Hope this helps a bit.