In Ocean's Eleven, during the vault robbery, Terry Benedict is shown a recording of a copy of his vault with the robbery in progress. The way I understand the time line, when this was happening Ocean, Yen and Linus were in fact in the vault. They could wear masks or something if they didn't want Benedict to recognize them. Why did they bother with the fake vault and the recording at all?
There are a few reasons why they would want to show Terry a video of being robbed, instead of showing him the live feed (or essentially feeding him a video of an empty vault):
1) They had to have a way of getting out of the vault in a plausible way. The fact that they managed to get in is one thing - but they also needed to walk out with a LOT of money. They couldn't go back the way Danny and Linus came, because they would have to go via the elevator shaft (which was rigged with sensors) and then via the hallways to get out the door (which have a ton of other cameras they didn't have access to). The only way they could do that was to have a situation where a SWAT team was called in; nobody was about to take a head count of how many SWAT members went in and how many went out.
2) They didn't want to show Danny being part of the group robbing the vault, because they wanted to allow for plausible deniability for him (remember, Terry still thought he was being beat up by Bruiser - though how he [or the two guards outside the door] could believe he was still getting a beating even during the blackout is a MAJOR plot hole). Thus, they didn't want to risk having Terry see Danny's face on the video (all Terry knew was that Danny had 'something to do' with the robbery - that could just as easily have just been in the planning).
3) Finally, as to why they didn't wear masks in the video - that was essentially a big "fuck you" to Terry. It was like "We don't care if you see our faces or not. We're MASTER thieves, and we don't go about robbing you wearing a bunch of masks" (unless it's needed to get away in a SWAT uniform lol).
Because only two of them actually broke into the vault, but to really threaten Terry, they need him to believe that they all broke into the vault and can do a lot of damage. And of course they need to fake a footage of SWAT attack later...