I've lived with a guy before marriage and I'm not sure it was any help. It's not a religious thing, it just can cause a bucketload of problems. there are times when it might be worthwhile to live together.
Here's an article I wrote ages ago and if you want to hear both sides, read the comments at the bottom of the page:
add your own comments if you want. In general, I think there are a lot of bad side-effects like just being too lazy to move on when it's time...let me know what you think.
On the other hand, my daughter is living with her BF and...in a very few situations...it might be good. they're both in college and they study together as they are trying to get into the same grad school program. My other daughter would not do well living with a guy.