Mood, speed, a game it reminds you of. Short is fine.
The chip new loops are written for. It sets the voices and the colours.
With a tempo you get four clicks first and the take lines up with the bars. On Auto it listens and works the tempo out.
Lands on the next bar.
Longer keeps the notes and adds empty bars. Shorter cuts the end.
The notes move with it, by scale degree.