Focus stacking is used to create a final image with greater apparent depth of field than a single shot can provide. By combining several photos focused at different distances, you can keep more of the subject sharp from front to back.

This is especially useful in macro photography, where depth of field is extremely shallow and you’re often working at the limits of what the lens can keep in focus in one exposure. In those situations, even stopping down may not give enough sharpness across the whole subject, so stacking multiple focus planes solves the problem.

In short: the main benefit is more of the subject appearing in focus when one photo alone can’t achieve it.