why not both? I know a few couples where one person often has their own place, but is never there. They keep it so they can technically say that they aren't living together with their SO. They're usually from a religious family and afraid of being judged by their relatives for 'living in sin'.
Some persons may have a sense that the faith tradition in which they were raised discourages cohabitation (e.g. considering it to be morally problematic), but: they're not sure why that's the case, they want to be with their SO, they wonder what's the best way to prepare for life together as a married couple (per the comment to which I replied originally).
So, on the one hand, I encourage such persons to learn more about why their religion (and/or the religion of their parents) teaches what it teaches[+]. And on the other, to recognize that there are good ways to prepare for life together that don't involve cohabitation.
