Shortly after the Atari was sync-ed up with the PO-33 using the joystick port clock output, the Atari MIDI output was connected to the PC MIDI input to monitor the data stream. I wish I could remember why.
That's when I noted that there was a MIDI clock ($F8) being sent from the Atari. I guess the manual wasn't lying. There was never much use for a MIDI clock to sync my arpeggiatorless MIDI equipment. Now I can see where it might be handy to sync the Korg NTS-1's and/or MicroKorg's