They lose branches and spread walnuts with nasty hulls everywhere.
Some years I pick up a five gallon bucket or more of walnuts every day for weeks from a single tree.
Black walnuts, while very flavorful, are much harder to shell than their English cousins.
Hope you like squirrels!
These trees also produce a poisonous substance called juglone that is toxic to many other trees and plants. Even after a black walnut tree has been removed, the juglone toxin may contaminate the soil for years. I have seen this happen in my own backyard.