When you don’t match the action in editing, it seems abrupt to the audience—and takes them out of the film. The worst example of this is something called a “jump cut.”  A jump cut occurs when you edit together two shots that are very similar. In the example at the upper right, you’ll see two shots of a man talking. The shots are so similar that the man seems to "jump" at the edit point. It's an abrupt edit. Watch it.

There are two solutions. One option is to replace one of the shots with a much closer or wider shot of the same man. But what if you wanted to keep those two shots together? A common example would be two sections of an interview that you want back-to-back.

So the second solution involves leaving the jump cut in place and "covering" the edit point with something different. This is why you often see TV news reporters nodding during stories. It's not so much that they want their face on TV, it's more that they need something to cover a jump cut. Watch the “solution” example.