FRCP 30(b)(6) allows a party to notice the deposition of a corporation or other organization on a list of topics. That organization then presents one or more designees to testify on its behalf at deposition. The designee's testimony is treated as that of the corporation.
At trial, it's not unusual for a party to want to play the 30(b)(6) deposition testimony of an opposing party, even if the designee who gave the testimony also happens to be testifying as a fact witness.
Why? Because, often times, the party got exactly what they wanted out of the 30(b)(6) witness on some topic, and if they play the video they can be assured that …