As a person who has lived with four people for a year or more, I have never found that I knew very much about living with them after a few nights or even a few months. These things, it seems to me, take years to figure out. Perhaps it is why there are so many divorces in the first three years of marriage. For women who divorce, around one-third of those marriages lasted five years or less (Number, Timing, and Duration of
Marriages and Divorces: 2001, Figure 3.)
For women, cohabitation before marriage leads to fewer marriages that end in divorce (except for people who have cohabited more than one time). This article says
“Cornell sociologist Daniel Lichter…. found that for woman, the odds of a marriage ending in divorce were 30 percent lower if they lived with their husbands before getting married; however, this is true only in cases where the woman’s husband was the only man she had cohabitated with before getting married.”
My guess that the reason this is true is that cohabitation lets you know how well you can get along with your partner. You need this knowledge if you want a marriage that will last. Women have got to see how loyal their potential husbands are.