There was a time, that ended about 5 years ago, when the repair tech was assumed to know both How and What. He could be assigned a repair job armed with only the information on the estimate. In most cases that information was only whether to repair or replace and the time that was allotted to the task. Based on prior experience he would be expected to know what to do. If he had repaired a bent frame rail many times in the past then the bent frame rail he was dealing with now could be repaired using that knowledge. With most cars using the same frame material and manufacturing techniques this prior knowledge was usually sufficient. Now, a vehicle structure can be made of many different types of steel and other materials, each of which have a specific design purpose and specific techniques for repair or replacement. All of this metal looks very similar and if the tech is not given full information about the materials used in the damaged area he will not be able to repair the car to Next Accident Ready condition.
This is no criticism of a conscientious and qualified repair technician. There is a tremendous amount of skill and knowledge in How, the What can only come from information provided by others. The damage report writer who is able to provide that What information is aware of the How, but would not be able to do it.
An analogy is the relationship between the orthopedic surgeon and the radiologist. The highly trained surgeon cannot do much with a sedated patient on his operating table if he is not given very specific information. The information he is given comes from sophisticated imaging technology that is best interpreted by the trained radiologist. The surgeon could probably read the images and determine what was needed, but the radiologist will be able to do it much more accurately and more efficiently. The two different, equally important skill sets come together to achieve the needed result, neither could do it alone.
The following post, with photos of a cutaway 2016 Honda Civic model, provides an example of how the How and What come together for successful repair.