The enhanced version allows for multiple assignments of a single object. As an example, in R3, a sales group can be assigned to multiple sales offices. In the standard organization model, this is not possible. As SAP’s CRM product has evolved, it has become more compatible with the R3 product. Before CRM 4.0, it was not possible to assign an organization object to more than one organizational object. This was a problem for many SAP customers because in R/3, it is possible.
So in 4.0 and after, SAP introduced the ability to handle multiple assignments and a program to convert the org model to this structure. So if your client has R/3 organization model that involves multiple assignments, you will need the enhanced version.