The primary purpose of Reference Sets are to provide a means by which, when working in a detailed part, that the geometry, generally a single Solid body, is part of the 'Model' Reference Set while of of the other geometry, which may have been used or referenced while defining the final model, is not included. This other geometry could include Datums, Points, non-sketch Curves, Sketches which were not made internal to the Model's feaures, Sheet Bodies used to trim or provide shape to the final model, etc. These items generally serve no real purpose when the Part Model is added as a Component to an Assembly and therefore the system, by default will use the 'Model' Reference Set which only contains that final Solid body. Now at any time, you can replace the 'Model' Reference Set with ther 'Entire Part' Referense Set if some of the 'extra' items are needed, perhaps a Datum or a Point needed to help position or constrain the Component, but once properly constrained, the Component can be set back to the 'Model' Reference Set without losing any links to the referenced, albeit no longer visible, items NOT in the 'Model' Reference Set. As such, this is how Reference Sets are recommended to be used, in the detail peice parts and NOT to control the content of an Assembly. While there is technically nothing preventing you from using a Reference Set in an Assembly to control which Components to include when using the Assembly as a Sub-Assembly in a higher level Assembly, it can cause problems later on when it starts to act like a 'filter' causing lower level Components from NOT being loaded when the top-level Assembly is opened.
So the rule of thumb is; for piece parts, use Reference Sets to control the content of what what is considered to make-up the Component when placed in an Assembly (if you do nothing, out-of-the-box this is the way Reference Sets will automatically behave). And for Assemblies, which will be used as a Sub-Assembly in a higher level Assembly where some of its components need to be seen in different positions or with different content in the current Assembly, then the use of Arrangements is recommended.
The bottom line is that you will need to be aware of both Reference Sets and Arrangements, but normally you can almost ignore having to worry about Reference Sets since they generally behave exactly the way you expect them to without having to do much work. Arrangements take a bit more effort but are very well behaved once you learn how and when to use them.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
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