In the interest of disclosure, I cohabited. But there were a few times when I caused problems (it took her awhile to be comfortable with me in the crib and the time her family visited and I had to bounce for 'appearances') and there were a lot of benefits (we got closer, had more time together).
But nothing substitutes for great communication, committment, honesty.
I mean, you have to willingly talk about everything. The toothpaste, sex, food, cooking, chores, expectations. Everything. So use that close time cohabiting ACTIVELY learning about your future spouse. It's not something to just smash her cakes at 4 am. You have to work and might as well start now.
Not to scare you but good relationships just don't happen. You work, fight, work and fight and hopefully have something else besides the person to hold onto. For me, it's religion, hope and the idea that this will work, no matter what. For others, they have something else.