|Image of a magnifying glass|
Via Flickr user Auntie P
There is also another advantage to captions, highlighted by the Daily Show with Jon Stewart. According to this article on User Interface Engineering, the staff of the show utilizes a computer program to search through old news archives to find clips of politicians to use on their show.
I think this could be handy for other things, searching for old news clips, television shows, etc. for quotes and lines of dialogue. It would be especially handy for the actual producers of the show to find previous references to old topics. So - yet another reason to caption those videos!