I personally don't think it's a good idea because there is more infidelity, child abuse, poverty, and violence among cohabitants than among married couples. Among live-in's who later marry, there is a greater risk of divorce than if had not practiced non-marital cohabitation. While most women consider it a step toward marriage, most cohabiting men consider it a convenient arrangement where they get all of the goodies (sex, cooking, housekeeping, companionship) with none of the obligations (fidelity, protecting, providing). The woman auditions frantically for the wife role, while her biological clock sounds louder and louder. She doesn't want to throw away a relationship she has invested years in, yet she isn't getting any younger. He is in no hurry- he can always find a much younger woman to have a family with. He is keeping his options open, stalling his marriage-hungry partner with a plethora of excuses. She walks on eggshells lest she drive him away. He holds the power in this unbalanced situation. She knows he can either ask her to leave or move out at any time. There is always one foot out the door, the attitude of, "I can walk away if my needs aren't being met." The longer a couple has been operating in this mindset, the harder it is for them to shift to the totally committed, stick-together-come -what-may mentality of marriage.
My husband and I had not planned to live together before our wedding- and ideally would not have. Our cohabitation period was brief- only six weeks while we wrapped up the wedding details (small daytime ceremony, officiated by a minister, outdoor venue). He had to leave his apartment because his neighbor was making his life hell (dumping water on her floor to flood through his ceiling, eavesdropping, thumping around when he was trying to sleep). He lived with his ex-wife for five years before their wedding 19 years ago (they divorced 7 years ago). She cheated on him shamelessly and squandered his money- facts verified by others. No cheating or money mismanagement here!
If an engaged couple cannot afford separate residences, they can each get a roommate of the same sex to share expenses.