In a rough analogy, Arrangements are to Assemblies what Reference Sets are to piece parte. Not a prefect analogy, but one that will serve most people's needs.
If your sister company (in Europe) has been using UG/NX for 10 years or so then it's quite possible that they were using it BEFORE we had implemented Arrangements, which BTW were modeled after 'Configurations' in I-deas and were implemented as part of the effort to provide equivalent functionality in NX both in terms of providing common functions as well as supporting the conversion of, in this case, I-deas assemblies which had utilized 'Configurations'. Prior to Arrangements, which were first introduced with NX 2.0 (2003) but not fully implemented until NX 3.0 (2004), many people attempted to use Reference Sets to control the content and positioning of components in sub-assemblies, but this was never what Reference Sets were intended for, so when the opportunity came along to implement Arrangements we didn't hesitate. Note that we had a similar solution under consideration at the time of the SDRC acquisition, but once we looked at Configurations in I-deas we decided to scrape our yet-to-be-developed approach and instead concentrated on implementing a 'Configuration' equivalent in NX and thus was born 'Arrangements' (the name change was due to TeamCenter having already coopted the term 'Configurations' for something else, so as to avoid confusion...).
Anyway, Arrangements are a key capabilities when it comes to defining alternative positioning and content of sub-assemblies which are used in multiple higher level assemblies.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.