I'm a little confused about when to play notes further down on the neck (like 6-11 frets). I had originally thought it was when you were going to be playing higher notes on the high e string, so you were already down there anyway.

However, I happen to catch a guitar show on t.v. where a guy was showing how to play a Hendrix song and he said something like, "this song is in b minor, so we'll play down at the 7th fret" (I'm not sure that's the exact quote or key, as it threw me off). I think he was actually barring the 7th fret.

Now my understanding is that b minor key would mean our scale of notes starts at b and the "minor" part tells us the pattern of whole or half steps we move up to get the rest of the notes in the scale. But can't all of these notes still be found at the top of the neck (frets 1-4)?

I'm confused -- please help me understand.

thanks,
Jeremy