Shooting in autofocus or manual focus is a personal choice that often comes down to the preference of the person behind the camera. Many new mirrorless cameras offer advanced autofocus settings that can automatically detect a subject and hold focus, making it easier to have in-focus footage. However, many filmers who grew up without this tech simply find that it's better for them to focus manually rather than depending on the camera’s autofocus to do the job for them. You also may need to manually focus if you have a specific vision that isn’t in line with subject tracking.