"From looking to mother nature around these parts.......for every ancient tree that has a wonderful root system there are a 1000 that don't have one. Some of this latter group is just as powerful looking as they tower up from the ground with only a hint of hidden roots....reaching for the sky and dominating the forest canopy some 50-60 meters about the forest floor."
Nebari IS the tree .. OK, well it's not all of it, but it is a pretty substantial part of it.
Bonsai is all about the first third of the tree's trunk--which the term nebari covers. Nebari is NOT just the roots. It is roughly how the tree's trunk grips the ground and emerges from it. That core is the plant's heart and soul; The seat of its personality; Its foundation. It's the frame from which all the remaining parts hang. It does alot more than accent the rest of the tree.
The top of a bonsai is ever changing because branches get too think, die off, etc. They are replaced rearranged, regrown, etc. with very little trouble. Not so with the nebari and trunk.
"Hidden" roots on a bonsai are like tits on a bull. They're useless--if they're even present. A tree WITH a beautiful set of roots and accompanying nebari IS ALWAYS more entertaining visually than one without. Why follow what the other 1,000 unremarkable trees are doing. The exceptional trees are the most beautiful...
Here's a test. Find a world class bonsai. What draws you into the composition at first glance? What makes those plants "special" to the eye? Is it the foliage? the limbs, the leaves? Ninety nine percent of the time, I'd bet it's the trunk...