#show interface summary command provides bandwidth utilization of each Cisco switch interface, VLAN and port channels. You can either measure bits per sec using RXBS/TXBS fields or packets per sec using RXPS/TXPS fields. Additionally you also get to know counts of pkts dropped in the interface.
#show interface gi1/0/40 command provides bandwidth utilization of a specific switch interface, which is good when you want to troubleshoot for specific case.
