A legal dispute is something that is much more reasonable than having everything dictated by 1138 pre-packaged state provisions. No one getting married has a clue about 99% of those 1138 provisions. It’s ridiculous.
In a cohabitation agreement you can specify these things as the couple sees fit. You can keep finances separate, have certain co-mingled accounts, divide assets, agree of division upon split, etc. This as mutually agreed upon terms between consenting adults. It is far preferable to the alternative.
Also, I don’t care about tax benefits. I wouldn’t sell my own principles and best interests down the road to the state for some cheap tax incentives.