Why do some aeroplanes take off with flap and others not?

Why do some aeroplanes take off with flap and others not?

Have you ever noticed how in your initial training, in the trusty single engine, you were taught to take one notch (10°) flap, yet when you moved onto a light twin engine, suddenly the instruction was zero flap? It can be puzzling why some aeroplanes take off with some flap and others with none at all, but the answer is an interesting one.