When shooting film they are the hard copy link from set to the lab. It lets the lab know if a scratch occurs they can look at other rolls from that mag to see if the scratch is consistent as Adrian said. They also let the lab know of any special processing that might occur. They are also hard copies for the loader to archive so if there is any confusion or questions it's written down. It allows you to go from the camera report to the film report which keeps track of total raw stock, exposed stock and short ends and recans. Every DP and 1st is different for what they want done and how it's done. Some rental houses make their own reports as well as labs. I got a great report template from a 1st where I was the loader on the show and just got used to that report.
Also, lens and t-stop are more approiate for a camera log. Which keeps track of all of that and lens height, scene, roll, etc.
Edited by Michael Kubaszak, 16 August 2011 - 06:12 PM.