What are the practical applications of "two will become one flesh"? Mark 10:8 (NIV)


  and the two will become one flesh. So they are no longer two, but one flesh.


What does this mean for a marriage?  What are the practical applications of this?  Obviously, this is an analogy, but what is it trying to signify?  Does sex play a role in this "becoming one flesh"?

a hint:

Does this mean that the needs of one will become the needs of the other?  Or that the happiness or sadness of one will become the happiness and sadness of the other?
It seems that "the two shall become one flesh" is regarding sex, although it could have other connotations as well.  

In 1 Corinthians 6:15-17, it says


  15 Do you not know that your bodies are members of Christ? Shall
  I then take away the members of Christ and make them members of a
  prostitute? May it never be! 16 Or do you not know that the one
  who joins himself to a prostitute is one body with her? For He says,
  “THE TWO SHALL BECOME ONE FLESH.” 17 But the one who joins himself
  to the Lord is one spirit with Him.


Here, it obviously refers to a sexual context, as it refers to joining with a prostitute.  However, the fact that it refers to sex should not down-weight the significance of "becoming one flesh", but "becoming one flesh" should up-weight the significance of the sex act, considering that the term "the two shall become one flesh" is used in the context of marriage.  The fact that it is also used in reference to engaging with a prostitute means that the act of sex is a very significant thing.