What does the black rectangle clipper when filming films and movies actually do? Why do they need one at all?

Question

I always wondered this

In: 133

Answer 1

It has a few.

One is that it has things like the scene, scene number, take number, etc recorded on it for the editor.

Another is that when it is clapped shut it makes a sound that can be used to make sure that the picture and audio are synced. It gives a very exact moment that the sound is produced.