Well, I gleaned that bit of info from some "how to YouTube" video years ago, and found it helped my retention... although I am sort of using it less now.
Longer explanation:
It has to do with the attention span of the viewer and the way the human brain works. Attention span is about 8 seconds. After about that, with nothing much on-screen changing, the brain starts to shut off, or tune out, the thing that you're watching.
Now, if you change camera angles or scenes TOO often, this is sort of what
@Theodor was talking about. The modern Hollywood fight scene cut. Way too many cuts, and you lose continuity. You don't know who's throwing what punch, or where people are in space, so it gets confusing. Also see: the 180 degree rule
So, the sweet spot is 4-6 seconds per scene. Enough to keep the viewer engaged, but not enough to be jarring. If you cut somewhere in that 4-6 second range, it reaches out and grab's the viewer's brain again and says, "hey, something new is happening - pay attention!"
In the olden times, motovloggers had 1 camera, and cut as needed, leading to jump cuts. With modern editing software and multicam setups, we have lots of options to HIDE the jump cuts. You'll see this in every single one of my motovlogs. I cut the blank space and switch camera angles, and voila - problem solved - not jarring jump cuts [at least, that's the goal].
Nowadays, we have a whole group of motovloggers who run multicam setups like me, and still some use 1 camera for the sake of the workflow [editing can be tedious and time-consuming]. I find their videos jarring, because they jump A LOT. Some do it every few words.
Pro tip: cut the blank space out, remove the video from the preceding clip, and smooth the audio between the two audio clips, and you have a much smoother video. I think I did a video on how to do this on my 2nd channel.
OK, so earlier I mentioned that I don't use the 4-6 second rule as much, and here's why. It's a faster workflow [less cutting = less fiddling, right?], and oftentimes I'm in full shadow, which requires me to tinker with the color [more time editing]. As much as I love editing, running 2 channels can be - and truthfully is - taxing on my time, so faster edits = more time for other things in my day, so long as the video quality doesn't suffer.
Sorry, not sorry, for the long post... and now that I've typed it out, I've copied it to a Word document so I can record a video about it. Thanks for coming to my TED talk.
-John