Monasticism: east and west

I'm working through Fr. Alexander Schmemann's Introduction to Liturgical Theology, and even having read it twice already, this is a valuable work that gives new insights each time.

Now the question lurking in my mind: what role has monasticism played in the church? I am only vaguely familiar with the development of monasticism in the west, and even less so in the eastern churches, but I'm intrigued by some of Schmemann's discussions about early monasticism playing a role of being the "outsider" when the church has had (say, in the years immediately after the Edict of Milan, in 313)to become an insider to the contemporary culture.

A more narrow question to me is whether para-church (usually, but not always, Protestant) are essentially lay monastic groups. I go on the assumption that there's nothing new in history, church history or otherwise. And I wonder if someone were beamed down from Mars, would a group such as Campus Crusade for Christ (now "Power to Change Ministries," the word "crusade" having fallen on hard times of late) look a lot like Rome's Opus Dei?

The crucial difference is the group's relationship with the church. My acquaintance with Campus Crusade in earlier years made me realize that these groups tend to function as church substitutes. I'm sure this is not the leadership's intention, but that's how it seemed to work out in real life. Groups such as Opus Dei, on the other hand, tend to be committed to the church's sacramental life. (The problem for Crusade may have been Protestantism's perennial problem with viewing the church as an academy for learning about the Christian faith, a view which -- historically speaking -- deficient).