Yes, init starts services at boot and stops them at shutdown. inetd, which is run from init, starts internet/network services when a port is connected to. If a network service is started by inetd then a new instance is started for each connection. Then when the connection is closed, the service exits.
If the service is run from init then it is only started once at boot and is always running.
You can run an ftp server from inetd if you don't expect much use as it's only really running when a connection is established.