The Importance of Prayer

I think that the question often arises though for people who have a view of God as having sort of essentially well God knows everything that's going to happen and possibly is even predetermined. So what on earth difference does my prayer make? And this is I think where for instance Janet in Wales is coming from a related question, does God know the future? Does he know the details of our lives in advance? For example, how we may suffer or our loved ones? And if he does, why pray? So it's that classic question isn't it? Reframed slightly.