Answer: To match the lipsing with the backstage voice artist.
Explanation:
The actor or actress working on state may not use their voice, while acting instead backstage people give voice to them. This occurs because the actress or actor at the stage may not give be attentive towards dialogue delivery or may forget the dialogues in public fear. Thus, it is advised that the actor or actress learn the script thoroughly and should not use own vocabulary or script during dialogue delivery. As it will not match with the voice recording of the actor or actress or with people working at backstage.
