In fact, ONE BUTTON CONTROLS IT ALL. Hit the Hold/Sustain (or whatever you set) once, shortly - and voila, the fixed-length fragment of what you play is converted to midi loop, synched to the host tempo. And it starts to play in the background immediately.
Transpose your loops on the fly (chord recognition included).
Make punch-in and partial erase w/ still same one button.
Use two additional controls for moar lulz.
Drive two synthz with it (one for loop, one for solo).