Hey Hey,

Take a look at the CCNP 4 curriculumn sometime.. The entire idea of the first couple chapters is that after you install a network, you establish a baseline so that you have something to compare to in the future when you run into problem.

You document things like traffic utilization, bandwidth usage, device CPU utilization, protocol distribution, traffic flows and error rates..

You do this after you first install the network and then at regular intervals throughout the life o fthe company.. Usually you'd dedicate at least a week to the monitoring..

This way when you have problems you can compare the problem area to it's original values and more easily pinpoint the problem.
this is actually a very helpful thing. A lot of companies dont bother doing it, but it is of great use, especialy when trying to show statistics when you want your comany to buy a bigger down pipe.