There are many reasons why an attorney would need to videotape a deposition:
1) It is a way to preserve the testimony in case a deponent dies, becomes too ill, lives out of state, runs away, or is otherwise unavailable to testify in court. The law in some jurisdictions allows for certain expert’s testimony to be presented by video, even if they are available to testify in court in person.
2) Video testimony is helpful for legal staff and expert consultants to gain a greater insight into deposition testimony as they prepare for trial.
3) Deposition video testimony may be used to impeach a witness if they change their testimony at trial.
Which do you think carries a greater impact:
Reading back from a transcript, or seeing the witness make explicitly different statements on the video than he did in trial?
4) When people know they are being videotaped, they tend to be on their best behavior. Sometimes hiring a videographer to record the event has a calming effect on disruptive attorneys and litigants. This lack of disruption means that you can do your job and get it done today, rather than finishing it off tomorrow