A structured cabling system can use the same cabling system for everything. Do you really want to figure out how to install and troubleshoot the phone cabling, then figure out the Ethernet cabling, then figure out the ISDN cabling? What happens when you revisit this in 6 months to make a change for two-line phones?
Long life- Structured cabling is an investment that will last for the long term.
Support for multi-vendor equipment - A standards-based structured cabling system will support your applications and hardware even after you change or mix & match vendors. With the proper structured cabling system you will not have to rework the cabling when you upgrade to another vendor or model.
Simplify moves/adds/changes - Need to move a computer or TV from one room to another. Add a modem connection to the office. Add a two-line phone, DSL, AND fax to the office. Share files or printers between computers.
Simplify troubleshooting - Even cables that were installed correctly can fail -- and they do. With a structured wiring system, problems are less likely to down the entire network, easier to isolate, and easier to fix.
Support for future applications - Your structured cabling system will support future applications like multimedia, video conferencing, and who knows what else, with little or no upgrade pain.