What will happen if I press the [BEAT◀] or [BEAT▶] button while the unit is in Scratch Cutter mode?

The speed of cutting will change. You can set it according to your scratch style. There are 3 setting values. The status of the light on the [FX/CUT] button shows the currently selected value:
Lit = instant cut
Slow blinking = slow cut
Fast blinking = fast cut