I don't feel there is any definitive purpose of rerecords.
We could say that it allows us to quickly identify movies that are likely low quality. Yet, actually it can't unless we look at other data. But that other data would already tell us the answer regardless of the rerecord count. For example, movies that are improvements on past publications. In some cases, but not all, the rerecord count is going to be very low. Does that mean that the movie is low quality or that very little effort was used? Impossible to say with just the rerecord number.
We could say that in light of some witnessed behavior in the movie, that the rerecords offers a quick explanation of that behavior. But does it really? We don't know which sections of the movie the rerecords are from. Did the author struggle in one part which turned out great, and then simply missed/overlooked time save in another part? Was the author just highly skilled or knowledgeable about the mechanics of the particular game? Or were they completely clueless? We can't know for certain with just the total number of rerecords.
It doesn't appear to me that rerecords are a good indicator of anything. At best, it can create speculation, doubt, or suspicion.
In considering what to say on this topic, I tried to calculate some statistics of movies on TASVideos (using the site's API). It was incredibly difficult to make any reasonable comparison based just on the rerecord value. To me, there's no obvious correlation between rerecords and anything else about a movie.
For example, here are two movies. Both are in the Stars class, both from the same console, of similar length, and both were highly rated by viewers as entertaining. Yet, when we compare the number of frames to the number of rerecords, they are entirely different:
What do the rerecord values tell us about these movies? Which one is better than the other? Which one had more effort and work put into it? The answers to these questions are not obvious.
Here's two more movies. Again both Stars, same console, both fairly long length, highly rated by viewers. Yet again, the difference in rerecords vs frames is significantly different. Additionally, compared to the two Genesis movies above, the rerecord vs frame differences are fairly similar despite these movies being drastically longer.
What do the rerecord values tell us about these? Anything? Nothing? Who knows. Only a deeper study of the movie will give us answers.