Lifestyle choices like cohabitation are always dependent upon the individuals and are to be respected. Many couples live together successfully and then go on to commit themselves to each other as husband and wife, but whether a couple lives together or apart before marriage, what's most important in a relationship is the presence of a spiritual commitment. Marriage changes everything, and the rationale that couples who live together compatibly before marriage can do so after marriage fails to acknowledge that fact. The lifetime commitment adds dimensions that are uncharacteristic of a couple who is unmarried and lives together. Cohabitating couples are bound by an agreement that is a lot like a rental contract (as opposed to married couples, who are bound by a contract that can be likened to owning serious property together).
In my work as a celebrant, I find that gender-associated attitudes explaining the "whys" of living together are superficial; the bottom line is that each person must be interested in caring for the other's feelings above all else. To me, these are the couples who are most concerned with building compatibility.