Originally Posted by Rusty Trichome
The more careful you are with the roots, the lower the stress. In other words, making a clean cut is less stressful than just ripping the roots apart. Never grown in bags, but have heard root bruising/breaking can happen during transplant, due to the shifting soils, but Psycho4Bud could likely offer more on this, since I'm pretty sure he grows in bags.
I do a good flush before transplant/root trimming to remove built-up salt and to keep ph in check, but allow to dry-out before transplant. This will keep the rootball somewhat intact for the move.