I wouldn't say it's necessary but IMO the videos never ever do it justice and frankly it's not even close. I'll never forget watching BF4 videos online and thinking graphically the game looked ok but I was more in it for the gameplay. Got the actual game and watched it on my TV and I went from thinking the graphics were ok to looking very good. I pretty much stopped watching all videos online for graphical comparisons after that.
The videos are good enough if one knows what they are doing (as Digital Foundry does). Not every comparison uses the same tricks, but DF gets the job done. And, it also depends on what is being compared. The differences between the Pro and PC versions of ROTTR have clear differences, for example. Most comparisons to PC will.