First and foremost I would like to clarify what a cut exactly is. I’ll try to explain this with a film and digital connection. First off, a cut does not have to mean that a camera moves. I also saw on a previous post that it meant a scene had to change. Let’s not confuse scene and shot. A scene/sequence is a collection of shots that usually pertain to one point in a story. A shot is one continuous period of time in which a camera was rolling and there was no temporal editing going on (there could be effects applied to one shot which is technically editing).
So the film and digital connection part. Think of there being two pieces of film. Tape those two pieces of film together. You have a cut. That’s why they are called cuts, because two pieces of film not actually “connected” need to be taped together. With digital film, think of there being two files (or clips). When you butt two files together without there being space between them, that’s a cut. That’s the basic definition of what a cut is.
Now about the camera having to move. I will acknowledge that this is the case almost 100% of the time. But there are things called jump cuts. This is where you break up a shot that would normally be one continuous shot into many similar looking ones. If you were to see a plane flying towards you and all of a sudden the plane goes from a mile away to 100 ft that is technically a cut. The camera didn’t move at all. But there was a cut. These are hard to detect but if you know about the term, it’s not too difficult to point out.
Now about the purpose of a cut. You do a cut because the thought and information in a shot are exhausted, as in you need to cut to something new. This is why when you watch a film there are cuts right after someone’s sentence is finished. They have expressed their ideas and we cut to a reaction. Interestingly enough you can cut in mid-sentence to someone reacting to the sentence. This would suggest that the person in the new cut is really listening because the sound is in the same frame as them (just a editing theory I thought of). One of the editing books I have read (“In the Blink of an Eye” by Walter Murch), Murch (who is one of the greatest editors who has ever lived) comments that when he was editing he noticed he was cutting right as an actor was blinking. He mentions how we blink whenever we are finished with a thought. So basically our entire lives are one big movie filled with millions of cuts. Just thought that was an interesting thing to bring up.
If you’re interested in editing I highly suggest the book forementioned and also the writings of Eisenstein and Pudovkin. The latter are hard to read (Russian translations BLAH!) but can be informative.