The reverse icon reverses the entire loop creating some potentially killer sounds. The eraser icon clears the playing loop without stopping the action or erasing your loop points. This allows for an on-the-fly break to silence. A popular way to use the eraser feature is to have layering enabled, and pressing erase just before you start a new theme, clearing the old to make room for the new -- hence instantly transitioning from one theme to another.
Keywords: VoiceJam: How to reverse / erase loops,VOICE JAM STUDIO