In my experience you have to know how to be a slave to be a good Dom. Though I suppose the same goes the other way. You know what is expected either way and can switch. Switches are complicated some have triggers to make them switch some can be forced some can do it at will. I feel that the ones that do it at will are just sometimes going for attention and aren't really a true switch they do it out of fun. Its a complicated question one that is not easily answered. There are Doms that have been slaves before tried that first to realize they don't have the mentality and vice versa. I myself thought that I was more Dom but with the right knowledge and reading a lot of material as well as experience I found out I was so very wrong. Its a yes and no sort of thing I guess it really depends on the person. I myself can "play" a Dom role but I have to force myself into that to stay there before I slip into a more submissive one. Its something I don't suggest toying with stick with what your stronger and best at. Just my opinion.