Whenever I repot my large Chinese elms, I save the roots and grow them into shohin and mame bonsai. Typically these roots have very interesting, twisting and meandering movements. By using these characteristics, one can grow mini literati, exposed roots and cascade bonsai with unusual twists and turns that are difficult to duplicate by wiring.
The followings are some examples of my mame size Chinese elms grown from root cuttings.
When growing bonsai from root cuttings, one has to pay attention to possible reverse taper because a cut-root is usually thicker at the top than at the bottom where the fine roots are. When new buds emerge at the cut-end, one has to select one bud to become a new leader and remove the rest; otherwise the excess buds would thicken the cut-end quickly and cause a reverse taper.
Many species can be grown from root cuttings such as ficus, hackberry, flowering quince etc. I like growing shohin and mame elms because their leaves are easily reduced to match the overall size of the tree.
Next time when you re-pot, before throwing away the roots, examine whether some of them have interesting movements that can be grown into literati or cascade bonsai. You can also wire long cut-roots with exaggerate bends since they are very flexible. However, I prefer to retain their natural shapes and style them into literati.