There are several different kinds of leaks:
1. raw footage somewhat random mix of cuts, some cuts end up in the official (censored) video, some cuts from different cameras (not end up in the release video) but during the actual sex scene, some cuts are just the camera recording for 10+ minutes pointing at a static empty chair while the cast/crew take a break. These come directly from the camera, had not been edited (i mean post-production, editing here has nothing to mosaic).
2. uncensored scene or part of a scene. Come from almost-finished-editing scene, they look almost exactly like the release video but without mosaic. Another, more likely, setting is the leaker had the full video (see cat. 3 below) but chop up to several scenes to sell individually.
2b. very short, low res, horrible watermark, cuts from cat.2 or cat.3 to proof that the selling has the good stuffs and waiting for a wealthy buyer. This kind is absolute garbage but because they are free they get wide-spread.
3. the full length completed-post-production release video except the mosaic has not been applied. (typically the studio do post-production (editing, sound-mixing, titles/end credits etc) themselves and then send out this version to another contractor to apply the mosaic, so there's a slightly higher chance of leak because this version is likely to be copied a couple times and transferred between a few parties) Needless to say this is the type of leaks that everyone wants.
One of the early leaks featuring Shunka Ayami showed that what looked like a 20 mins sex scene took more than twice that long to film with a lot of interruptions, breaks, repositioning the camera/lights, touching-up of cosmetics etc. It shouldn't come as a surprise, but it was... Prestige (esp. that Absolute XXX series) production are always super-polished and beautifully produced. But the viewers can also kinda sense that no one actually had any pleasure during the entire filming.
So needless to say, it's very disappointing leak as far as the pornographic value is concerned. But once I got over that (it's never any real difficulty to find another JAV to fap to) it's really interesting to see how the sausage is made, as Brits like to say. It explain why I always want to watch Prestige vids but when actually watching it, I get bored and switch to a second-rank studio with a second-rank idol.
I am also rather interested that a lot of the filming activities and people involved are actually quite boring. Correct that, I'm interested to see any raw footage no matter if it's fappable, exciting or super boring. Of course if it's boring, it's not worth keeping but I'd watch it at least once.
As for the fappable leaks, esp. the Cat. 3 it's great to find them (which is rare, for both good and bad) but ... well to be honest, it's usually not as good one imagines. Actually what becomes most in-your-face after finding a leak is the cock. Some fans may actually become disturbed by the sight of un-mosiac'ed cock. Not I, while I don't love cocks, I enjoy seeing hot women get dick'ed by big fat penis. I found, mostly, the best part is raw blow jobs. When it gets to vaginal penetration mostly we see condomed dicks. It's fine, it's totally within reason. Why should idols accept raw fucks when it's all gonna be mosaiced anyway? But somehow because I got used to seeing mosaic, the mind kinda forget all kind of camera tricks are hidden under there. So when actually seeing condom it's kinda... irrational disappointing. Once in a while you see condom and (fake) creampie, which of course... broke the internet. (and if you take a minute to think about it: the stud comes to work, has to get himself erect on demand for all day, and go home without even ejecting his load, because the filming wanted only fake cum) I think... only 1 out of 4 leaks are really good for fapping.
I mean... come on... it's a performance, it's film making. The porn-maker's promise is only to help you fap, there should be no misunderstanding that everything is real. Fake tits, fake dick, fake cum. I already accepted porn is just an image, not reality. So instead of getting angry over fake dick or fake cum, I'm actually very pleasantly surprised that many of my fav idols are very professional about sucking raw dicks. Esp. real ejaculation in mouth or on face.