Many years ago I got an education in repotting from Ripsgreentree. Glenn explained that taking back roots with a cleaver was much better than just nipping away root by root for mass reduction. I still use the small pruners on my more developed maples and elms, where they have a more fiberous root structure rather than a coarse root structure. Those first root reductions can be made much easier with an appropriate cleaver to just “one whack it” and then wash the root ball. As the years go by, the roots get finer and scissors becomes the tool of choice then.
The real trick is placing your finger over the parts of the roots you want to keep, forcing your mind and coordination to strike in the correct place. If your off a little you can always grow back a finger, but chopping roots to short is a no no….err is it a lizard that grows back something, oh I forget.