In some cases, it may not make sense for all traffic to be trunked to all switches. For example, consider the network diagram shown in the figure below. In it, Switch C does not have any ports configured on VLAN99. As such, it doesn’t make much sense for traffic destined for VLAN99 to be sent over the trunk link between switches A and C. In order to control traffic destined for VLAN99 from being forwarded to Switch C, you can enable VTP pruning. Once enabled, VTP pruning will stop unnecessary traffic from being forwarded to a switch with no configured ports on that VLAN. If VTP pruning were enabled in this example, traffic for VLAN 99 would not be forwarded to Switch C by Switch A, thus conserving bandwidth and switch resources.
By default, all switches have VTP pruning disabled. When enabled, VTP pruning enables the function for the entire VTP management domain. If you do choose to use VTP pruning, note that you also have the option to go a step further and define which VLANs are eligible to be pruned and which are not.