I can never find info about what to do with roots that appear growing down through the drain holes in a pot. I have a dracaena marginata which is in a pot with drain holes inside a higher pot without holes, so that it doesn't sit in water. It doesn't look root bound at all except for the roots coming through the bottom, some are quite thick. Should I just leave them alone which I usually do, or can I trim them off from the outside of the pot without damage? Or is it a sign to repot? Always wondered about this so time to ask!!

No, not a sign to repot or that the plant is rootbound. Roots follow the water out the drain holes. If pots are sitting on the ground outside, plants will root into the ground. The cache pot makes a good humid substitute. I don't know if it would harm the plant to remove those roots, I always leave them. Cutting them off will slow growth as the plant can only grow as many leaves as the roots can support.

Thanks Daisy for your reply! I keep most of my plants in raised cache pots, and see the roots dangling down quite often. Never quite sure if it was a good sign.