The other day I drove by one of those speed measurement devices. As I passed it, it gave me a digital readout of my speed (and a good dose of radiation). The intent was to let me know how fast I was going. That way, the police hope, I'll think about my driving speed.
If the road were a network, then the speed device would be equivalent to a network management package. Like the speed measurement device, a good network management package gives you the ability to watch packets speeding around your network.
Understanding traffic flows in enterprise networks requires advanced network management tools such as Concord Communication's Network Health or System Management Arts' InCharge. Those packages can tell you a great deal about the internals of your enterprise network and help assure the enterprise's overall health.
Unfortunately, the packages are expensive. That makes them a tough sell, especially when spending the same amount buys an additional router or switch. However, network tools are often a better investment than new hardware because they provide an early warning system about developing problems in the network.
If you can't afford such tools, you can go the poor-man's route and get network statistics through RMON (Remote Monitoring), Telnet, or even Multi Router Traffic Grapher (MRTG) , a tool that monitors traffic load on networks. They're not as elegant as Network Health or InCharge, but through the use of scripts or basic SNMP reports you can obtain much of the same information provided by the more sophisticated tools.
Either way, it is a good idea to keep an eye on traffic trends in your network -- just as the police want us to monitor our speed.