There are three aspects to this
1)Judical - is cohabitation bounding you before law in some way in your country or not. This is country dependent so see your laws.
2)Psychological - how it affects the future perspective of your lives and chances of successful marriage. First of all you should be already 90% sure she is right for marriage before cohabiting. So there should be not much issues left to make sure about her. Of course some things can get revealed only with closer contact. Is she attractive enough without makeup, does she loves domestic chores, can you manage money and free time together, does she give you enough space? I would say you must cohabit but make that cohabitation period short, like under one year. You must decide during one year if she is good for you or not. Risk is you stay longer with her out of convenience, then marry her out of convenience while not really happy and miss something better, you should avoid that. Basically cohabitation is the practical form of engagement when you are already planning marriage.
3)Religious - for people who do not want to look at psychological aspect and rely on priests to provide it for them as a religious rule. This priestly advice can be well meaning but sometimes not keeping up with the times. Religious advice says you should not cohabit before marriage but these rules were written in much better times when when social morals were high - a women would never be living alone. She lives with parents when single and with husband when married. At worst she would live in all female dorm where an old lady would watch them them to come home by ten o'clock evening. This advice is not working these days because in old times the whole society worked to make it easy for the girl to guard her virginity. Since in this age society makes it easy for girl to walk around and slut around - the sooner you take her under your wing the better. Do not let her live alone and be dragged to late parties by girlfriends for too long. Also please note that cohabitation can be separated from sexual intercourse if you care about being chaste before marriage. Of course it takes some willpower, but again - you have a better chance keeping her faithful under your wing then living alone. However keep the cohabitation short or she will start seeing you as an asexual brother or girlfriend if you live with her too long without sex.
Summary - absent some laws that might twist all of this - do cohabit, but only with a girl who has no red flags and you would probably marry anyway, and keep it short, in one year's time maximum you should split up or marry. Have sex during cohabitation or not based on your religious views and willpower.