The Maximum Utilisation input tells STEM to install an additional variable amount of slack capacity (usually bandwidth) in proportion to the nominal total demand to allow for transient peaks in usage.
Example
The traffic for an increasing number of customers is aggregated at one point of presence (PoP) and needs to be carried to the next network element. Although a contention ratio is assumed, the planning rules for the network allow only Maximum Utilisation = 80% for the circuits; thus, a standard Fast Ethernet circuit with a capacity of 100 Mbit/s can only be used up to 80 Mbit/s. If the estimated traffic exceeds this limit (or multiples of 80 Mbit/s), then an additional circuit must be installed.
See also 10.3.18.1 Maximum Utilisation and Deployment.