I do think it makes a difference being married. Standing before witnesses (however few) and making a solemn commitment to another person might just take you through some dark times. I do think being married might make a difference.
There are also other considerations. Mostly financial.
If you have children and have taken a subservient career (gone part-time, had a career break, become a SAHM, or adapted your career to better suit your family) in order to look after your home and children and you are unmarried, you are a complete fool and have totally ignored the potential and very real consequences a break-up would have on yours and your children's financial future. The state will likely end up paying for your foolishness. Aside from Child maintenenace which is paltry, your ex partner would have no repsonsiblity to your financial welfare or housing needs.
If you are married and split you have a right to a 50:50 share in all assets. And if it's still deemed likely you can't cope financially on your own, you will get mainenance or a larger share of the assets to help you on your way, possibly both. You will also get a share of your ex spouses pension.
If you aren't married, you will get the children and your ex will walk off with his job. If you have two children, he will keep 80% of his net income and see the children every other weekend. You will keep the children for 95% of the time and receive a 20% net contribution from the absent father and the rest of your income needs will have to be made up by either you working (difficult because of the high cost of childcare) and state assistance.
The Tories are bang on the button incentivising marriage. Because the state picks up the tab for feckless arsehole men who end up in the pub and the money could be put to much better use.
And I see the ghastly Balls has climbed on the bandwagon now anyway. No wonder the Tories are trying to keep quiet about their policies for as long as possible. Do Labour have ANY ideas?
In short you should only be cohabiting if you are the main breadwinner.
It isn't only a piece of paper.