If you gave an object the property "„object is visible in case of voice extraction” (see the capella 8 hint in the September newsletter), then you read a strange question afterwards:
This is very easy:
Maybe you want this object to appear at a different position in the voice extraction, for example below instead of above the staff. To do so you are creating two objects: One at the position in the voice extraction and a second one at another position. To avoid that this object is lost as you won't see it any more when switching back to the entire score this message appears.