I believe the first take is for people who work in VS, the press, bloggers and so on. I think that's when they have the cameras on stage with the girls and then the second taping is for the celebs and special guests, maybe family members of the Angels? They do it to get extra footage when editing the show and getting it ready for TV. Like if there is a mishap during one of the girls' walk, they can use the footage from the other taping.