Yika,

External References are a powerful feature in CATIA V5 when doing Relational Design between parts and assemblies, amoungst one or more users. But this requires that your company develop their own methodologies and standards (along with good training) to make sure that everyone understands and follows the standard practices.

A good source of information is a 4-part series of articles written by Julie Cyrenne at Dassault, and published on the COE NewsNet last year. Here's the link to the first article:

http://www.coe.org/newsnet/Feb05/tips.cfm