Psychologically, it may be a danger.

Low self-esteemed people tend to take things more deeply than they show on the outside. A simple word, or a phrase, or an arguement during a scene or everyday life between the Dominant/submissive could cause that person to be hurt far beyond they would show.

Best advice, use caution. Try to touch on their feelings at the start, and adjust your approach to those feelings. Learn that there are certain things that you'll avoid with this person, no matter what, because they CAN hurt this person.