Cohabitation is much more prevalent in the western world.  There is increasing acceptance to the practice now.  In the years gone by, it certainly was something that was frowned upon and opposed vehemently.  Even today, there are groups who oppose them, especially religious ones.  Those opposing cohabitation argue that it trivializes the institution of marriage.  According to them, couples take their relationship less seriously in a cohabitation situation and are less likely to really work at their relationship - as opposed to if they were married.

As far as benefits go, well I guess one of the reasons why couples choose to cohabitate is that they want to get to know the person more completely.  They may want to know whether they would really be compatible with each other.  There are certain aspects of a person you don't really know until you are living with that person 24/7, that's one argument put forward.  Maybe cohabitation tests compatibility the best and could perhaps save future discord.  Some couples may consider lack of commitment as being a benefit.

Certainly, there might be serious consequences to cohabitation in other countries (non-western ones), but I don't know of any consequence that exists in the western world.  In much of the world, cohabitation is taboo.  I think in some Islamic countries it is illegal - I don't know if it is punishable by death though - could be!!! 

I personally don't believe in cohabitation.  In some cases, there might be reasons why couples can't marry and so choose to cohabit - I can understand that.  But, other than that, I don't believe cohabitation really benefits in any sense.  I would like to state though that this is just my personal opinion - perhaps I could be wrong.