To begin, we must keep in mind every SAP implementation is different. That is because every business is different in the details related to their individual business processes and/or master data. Even with in the same company or entity, there can be slight or major differences in a business process or master data based on an enterprise slice. Some parts of the organization perform business one way, while another performs business another. While this is a challenge during implementations, SAP has delivered many different enhancement options. These may be leveraged by the design and development teams to meet the needs of the organization. Enhancement options are always preferable to core modifications when possible.
SAP NetWeaver 7.0 (formerly 2004s) offers the new Enhancement Framework that not only is intended to unify the modification and classic enhancement techniques, but also offers you almost the same flexibility as modifications without the limitations of modifications.