There are two basic different types of what you are asking about, Deane.

The first, where you input these chords in advance, and save them to be used for later is usually called a Chord Track.

The other, once a Roland feature, and now used by Korg in the PA3X, is called a Chord Sequencer, although that's a bit misleading name, as it is a live, realtime feature, rather than how we usually think of a 'sequencer'.

In this, while you are playing, you hit a button for Record, and it only records the chords you play... Then, when you press Play, it immediately drops out of record, and starts playing the chords, looped to the length of what you played.

So, you play the head, or verse and chorus, hit play, and now BOTH your hands are available for whatever you want. If you hit the CS 'Stop', it doesn't stop the arranger, just the chord 'loop'... and you can play a bridge, vamp, whatever, then hit Play again and the loop starts up again...

I found it possibly the most useful thing an arranger could ever have. Why Roland dropped it is beyond all reckoning!