Repotting is done for several reasons: to work on and prune the roots, to change and refresh the soil, and to adjust the planting angle. Sometimes all three. Here are a few examples of each.
First up is a “normal” repotting of a Chinese quince, which is pot-bound. All soil is removed, roots are trimmed back, and heavy roots are removed from underneath the base. The tree is secured back into the same pot, and fresh soil is worked in:
This Ume only needs fresh soil, so very little root pruning is done. A couple dead roots are removed, and thoroughly rake away compacted soil from under the base of the trunk. Then the tree is secured back into the same pot, and fresh soil is worked in:
This itoigawa was restyled last year, and the planting angle was changed significantly. To change the planting angle, it will take several repotting efforts to get the roots on the new horizon.