I think the deal is we can still learn from photos and vids. But you have to realize and take into account parallax. (the perspective you are looking at something at i.e. how traintracks look to NOT be parallel when you look "down the tracks")
Also, as per a thread like mandrin's "Invisible Exertions", the golfer's intentions are not known. And subtle things, often tough or impossible to see (or identify) with the naked eye or even images, can make big differences.
Was just thinking about that today actually. Brian has said his "best looking" swings often produced the worst results. And the "ugliest" swings often were the best!
I can make what to me are big changes, and see an improvement in play, and it might be tough to see on video. (esp if you didn't know what was changed)