I have a pretty high backswing (if I were standing straight up it'd be around shoulder high) and it is a little assisted. It's accentuated by the forward lean of the body though. I don't know that I could really speak about the pros and cons per se, it's just the way I bowl. If I'm a little rusty or out of form, I tend to lift the backswing a little too much, which I can feel in my shoulder as it becomes uncomfortable. I think I'm lucky enough that when I lift the backswing, I lift it in a straight line, if you can do this, I don't see an issue with it. There are a number of the touring pros who aren't even close to relaxed on the backswing, it's the forward swing where it's more important (in fact when I did a coaching course with him, Dick Ritger said that one of his methods for increasing speed was to push the ball in the forward swing a little (stopping before the release point))
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Reporting from England