I need a new outdoor unit, but my indoor unit works fine. What are the advantages of replacing my whole system at the same time?

Air conditioners are designed as matched systems, with an efficiency rating given for the whole system. If you replace only one part, you do not get the advantage of many technology changes that make the system work efficiently to ensure comfort. Also, the indoor system contains a cooling coil which may be partially blocked by particles that will decrease efficiency. Further, if your whole system is replaced, you will be less likely to need service in the near future.