You can see all the type of packets that pass through the network. It is very helpful for you to understand network protocols, such as their formats, headers.
you capture others network activeity.for exmaple,check which website your boss is visting,who is busy accessing whose shared directory.
With deep understand of all the protocal,you may even fake some packet ,but is very hard.
you can also resolve enum all physical/IP address on th network.