As a "general rule", avoid pinching bonsai. It's usually better to let it grow, and cut back.
Letting it grow stimulates the roots to grow. Good roots make for a healthy tree. Pinching tends to inhibit the production of auxin, the hormone which stimulates root growth. So, pinching the top retards root growth.
Letting it grow stimulates the roots to grow. Good roots make for a healthy tree. Pinching tends to inhibit the production of auxin, the hormone which stimulates root growth. So, pinching the top retards root growth.