Cohabitation...a bad habit?

Here's the deal.
Catholics (and many Christians) say: Cohabitation is wrong. People should not live together until they're married. Living together denotes sleeping together, and sleeping together (before marriage) is a sin.
Others say: Cohabitation gives a couple the time and experience they need to see what living with one another will really be like, to see the annoying things each does, to weigh the options of a more permanent commitment like marriage. When you do something like moving in together, though, that does really complicate things if and when things go awry and break up ensues.
Still, I wonder.