I am one of the folks who requested a retabulation several years back on L3 and bchad is correct that they do not actually regrade everything, they just make sure the points were totalled correctly (hence the term retabulation instead of regrading). I can’t speak for anyone else’s decision to have or not have a retabluation done, but in my case I assumed there was almost no chance that it would change my score. The important word there is “almost”. I was comparatively old when I took L3 and knew I didn’t have too many more shots at it due to real world demands. I was also well established in my career and financially comfortable, so $100 wasn’t going to alter my financial situation in the slightest. So, $100 was worth the infintesimal chance that my score was not tabulated correctly. I was also band 10 and my 40/60/80 score was better than a lot of folks who had passed, so I thought one or two missed points might be the difference. Unfortunately they were not, but at least I knew that I had failed because I didn’t know the material well enough and not because some tired grader forgot to include the points from part 4 of an 8 part question in the question’s total score. I retook the next year and passed though and never missed the $100.
I would not have paid for a retab at L1 or L2 though. I also don’t think CFAI offers the retabulations as a way to make extra money. If you read their description of what they actually do and don’t do and how the initial grading is conducted, it becomes pretty clear that it is highly unlikely a retab is going to yield a positive result. I suspect they offer it to avoid being sued by hundreds of people per year who think they passed.