1. To stay connected to IRC 24/7. Even when you close mirc the psyBNC will maintain your connection, so when you connect later, you'll instantly be back on the channels you left.
2. Hold your nick or op's in a channel.
3. Hide your IP address, even in DCC connections. In other bncs, a direct client-client session is opened, revealing your IP. With psyBNC the connection is bounced through the shell with your IP remains secure.
4. You can connect to mulitple networks and link psyBNCs together.
5. ZNC is a newer and probably better bnc program, slightly different but probably worth trying. (type get-znc -v from SSH to install)