If you didn't have some stage fright or performance anxiety, then you would not perform well. We need a moderate amount of stress, or performance anxiety, in order to perform at our best. There is a relationship between stress and performance, known as the inverted-U curve:
So when you have no stress (comatose) or have too much stress (panic attack), then you have the lowest level of performance with each of these extreme. But as you see from the graph, moderate levels of stress leads to optimal performance.
So moderate levels of stage fright is needed to perform at your best.
