I rip the roots apart with my hands. The idea is you want the root ends to be pointing out instead of back into the root ball. I don't know if it's the best idea, but it always seems to work.

I used to gently tease roots apart with my hands. Than with hand rake. Than I started making few vertical cuts into to root ball. Now I take a sharp knife and chop about 1 inch thick vertical slices on four sides of a root ball. That last method, though brutal, works like a charm with potbound shrubs and perennials. I never lost a plant due to that treatment, I did however lose plants that I left with root circling and they never grew into native soil.

No need to process roots on herbaceous plants, these do not produce permanent roots that remain in fixed positions. And they are also more likely to be adversely affected by root damage than woody plants.

If you have anything with crown gall now you want to remove and destroy (burn or place in trash) the infested stock and stay out of the spots where these were present. Crown gall is spread by moving around infested plants and infested soil, probably does not require the level of damage of cutting roots to infest plants.