In protocol design, why would you ever use 2 ports?

Question

When a TCP Server does a socket accept on a port, it gets a new socket to work with that Client.
The accepting socket remains valid for that port and can accept further

Answer 1

Like many of the older wire protocols, FTP is suited for use by humans. That is it is quite easy to use FTP from a terminal session. The designers of FTP anticipated that users might want to continue working with the remote host while data was transferring. This would have been difficult if command and data were going over the same channel.