What is the new sync on beat feature actually about, what is the difference to before ?
While the original synths received and followed master clock, they did not have midi beat sync. Meaning you couldn't accurately sync up the arpeggiator or sequencer to an external drum machine via midi unless you played 100% accurate or perfectly hit the keys or sequencer button on time. This new feature (Which is now part of nearly the whole Sequential line-Prophet 6, OB6, Prophet X and Prophet REV2-and will likely be implemented in their synths going forward) means you regardless if you hit the keys or play button accurately, it will detect a beat and sync up to it automatically. It's really been beneficial for me.
I did this track and the middle part has the arpeggiator on the Prophet-6 perfectly synced to the Tempest.
https://soundcloud.com/user-523209234-123574856/night-of-1000-screams-prophet-6-prophet-x-moog-sub-37-tempestThat being said, the sequencer jack on the back of the P-6 is actually meant for beat detection if you are using a CV type setup with kick drum feeding each step of the sequence or arpeggiator.