Japanese recommend to remove all old soil when repotting.
They use a chopstick and carve away all soil in between the roots. Is that not bare rooting?
Just one example. They all do this.
http://satsukimania.net/index.php/tips/repot.html
All satsuki bonsai books I have seen recommend exactly this.
In Japan, the Satsukis are often bare-rooted.
But Japan's highly humid climate is the home of Satsuki bonsai. The rest of the world, not so much.
Here is what Robert Callaham says, in his Satsuki book:
"..such seemingly casual treatment was deemed adequate to maintain viability of roots in Japan's highly humid environment. In a Mediterranean climate, such infrequent moistening of roots probably would result in significant mortality of exposed roots.."Here, he refers to Mediterranean climate (my climate), and I know that many of us live in a climate that is not Mediterranean. But the point is, we, outside of Japan, need to be more conservative in the way we treat the roots of these plants, because our climate is never exactly the same as the one in Japan. I've learned the hard way, that some plants behave very well outside their homeland, but some plants become very touchy in a foreign climate, even just slightly different.
I am sure that most of the time, a careful bare-rooting would cause no problems, but "most of the time" is not good enough for me. I want to make sure, that a problem
never happens.
The book also says that even in Japan, the top of the root-ball is treated with extra care, by covering the potting medium (after repotting) with an extra layer of mulch. This will keep the top layer moist at all times, which is necessary to develop the strong surface roots.
This is why I leave the live moss intact on the top of the rootball, if I already have a nice and perfect nebari. If there are faults to be corrected, then of course you have to do some combing of the top layer of surface roots, and then apply the mulch for extra protection.
P.S.: Just to put the above in perspective, one often hears that you should never bare-root pine trees. This is a good advice, but I've often dug out field-grown pines in my backyard, and they ended up being bare-rooted, because the the entire soil was shaken out of their rootball. And they did just fine after being potted. But this success doesn't mean that I will bare-root an old pine. The extra care is always important, when we work with a valuable tree.