I trim the long fibrous roots short enough so they don't cross each other.
When I worked for a large nursery we trimmed hundreds of roots per day and
used pruning shears for bundles of small trees and shrubs, lopping the long
fibrous roots off as they dangled down, we cut them short, to within a few
inches of the main root. Sometimes this meant cutting 80% of the root
length.
I don't worry about cutting a lot off of thin fibrous roots, I don't think
they contain that much in nutrients whereas larger firm roots do, (I usually
only cut the ends off of larger roots to make sure they have a clean cut)
I hope this addresses your concerns
Kevin Bradley
Edible Forest Nursery
zones 3, 4, and 5