I am not sure where to ask this so I placed it here. Sorry if its wrong!
Yesterday I was noodling with a mate and he asked a question that I am not sure of the answer:
When do you know what type of chord shapes to play EG: barr, power or open. I usually just play around till I find what makes the song easier to play - But is there an actual code or rule to help you distinguish the difference.
Not really, you just use what sounds best for what you want to do. If you're covering someone's song and want to reproduce it as closely as possible then that means finding what the original artist used but if you're writing your own material then there is absolutely no rule whatsoever.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”

no rules. using chord positions that make the transiton to the next chord easier is always a good bet. you also may end up using a chord shape found in a scale when going from a lead back to chords once again for easier transition. certain chord voicings work better with distortion so that is something to keep in mind. otherwise when writing your song your rules.