I am experimenting with using ref geometry sketches to create a top down design and am a little confused about how to create the reference sketches.  I have been creating a ref geom PART with several ref sketches, then inserting that PART in each PART / Sub-Assembly / And Assembly.  This (I think) allows a change to the ref geom PART to propogate down to all PARTS and Assembelies.

I get confused with what sketch geometry to put in the various sketches in the ref geom PART.  It seems to me that some sketches should only reference the shape of PART sketches and PART features,  while others reference the positioning of those parts in Sub assembelies and Main Assembelies.

I am really unclear about inserting several instances of a PART into a Sub Assembly because that Sub Assembly has the ref geometry Sketches from the PART inside the sub Assembly and the PART inside of the PART instance.  Once the instance of a PART is inserted into an Assembly should I be using sketch relations or Mates to locate the part?