Computers can do it! Why can't we? Pushing a button to undo time is an easy fix I realize. Tinkering with the space-time continuum should never be so simple.
It would come in handy for instances when you are painstakingly painting something in ink. As you are putting your brush to the paper to paint your last few strokes, you realize that you didn't take some of the pigment out of the brush. The color will be too saturated! The Brain frantically sends the message to Hand: "pull back! pull back!" but the Hand continues on its course, and by the time the hand receives the transmission and reacts, it's too late. As a result, need to redo the whole thing. Just saying.