You have seen a bunch of opinions as to why. Here is a take on what usually happens.
I have done many a field review and I can say you really have to screw up for me to go to “Section II”. That of course, is where I disagree with the value and ultimately, the appraisal’s quality to rely upon. It is a rare occasion where I find zero mistakes or inadequacies. Many times I may disagree with the exact number but unless I can prove they are wrong, I chalk it up to 2 competent appraisers coming up with 2 numbers and leave it alone.
Usually they are minor errors (typo on taxes/flood map/lot dimensions). Most issues are failure to summarize. On a 1004, you have to summarize your data. Just filling in the fields and checking off “highest and best use” is not enough. Description of the neighborhood and market is also frequently lacking in detail. However, in the vast majority of the cases, I agree with their data and conclusions and end up stating, “this report can be relied upon”.
If section II is not needed and the Reviewer says it can be relied upon, nothing will be done and you may never even know it was reviewed.