Why? Since the programmer at Adobe probably isn't going to pop in here and explain, we will probably never know.

Quality levels between 92 and 100 probably are the same. There really aren't 101 different quality levels, there are probably only 13 distinct quality levels.

I had major problems using file-size limiter when I tried it (a good while ago, probably Lr3)

Inexplicable results, and worse - inexplicable errors.

Perhaps some people have had better experiences with it?

Rob

that´s old news.

http://regex.info/blog/lightroom-goodies/jpeg-quality

Conclusions

First of all, you can't directly compare Lightroom's JPEG quality settings with any other application. The settings may well map directly to Photoshop's save-as-JPEG 0〜12scale, and they may well partially map to Photoshop's “Save for the Web” settings, but all bets are off when it comes to the JPEG quality setting on non-Adobe applications. They're just totally unrelated to how Adobe does it. (I should make it clear that the difference is neither good nor bad; I've presented nothing here about how any other application creates JPEGs, so there are no conclusions to draw about which might be better or worse than Lightroom; the important point is to recognize that the scales, even if sharing the same “0〜100”labels, are absolutely completely unrelated.)

The Lightroom default JPEG export quality of 75, falling in the 70〜76range, seems to provide for as good a visible result as the highest quality setting for all the samples except for the bridge, which seems to suffer at least slight posterization banding at all levels, including even“lossless TIFF”. The file size, even at this relatively high 70〜76setting, is still about one third that of the 93〜100setting, so is well worth it in most situations. Those who blindly use the maximum setting for their exports likely waste a lot of local disk space, upload bandwidth, and remote storage space. But conversely, those who blindly use some lesser setting risk posterization in the occasional photo with an unlucky sky gradient.

yep possible you encountered a bug with the 100% setting.

Agreed that the file size limitation in both LR3 and LR4 simply does not work, giving significantly lower file sizes than what is input within the export dialogue box. Use the save for web command within PS if you need to limit file size.