Screencaps are great because they let you preview the video without sitting through minutes of "fast forward" content that may not interest the viewer. If they don't see what they want in the screencaps, they move on to another video rather than waste time watching.

I did that for Bedfellow before watching the video.

Now... screencaps AS content without the video to accompany it is questionable. In that case, it would be better to use full quality professional photos for clarity.