A lot of “experts” suggest you should stick to one genre. To expand your repertoire from, say, sci fi to romance, dilutes your following and makes it necessary to promote in more than one stream.
Yet many writers ignore this “rule” successfully. Sometimes they publish under pen names, and sometimes they don’t. Sometimes the genres they write in are related, and sometimes they are wildly diverse.
Sometimes they break the mold entirely and create a whole new genre, or sub-genre. Books are something like people; though they have certain features in common, each is unique. It is the uniqueness that we find captivating. So why not write a zombie-distopia-shifter-romance if you can manage it?
I write the way I read: omniverously. I don’t plan it that way. It’s just the way stories come to me. Would you call yourself a cook if all you knew how to make was spaghetti sauce (even if it was the best spaghetti sauce in the world)? I doubt it.
I believe every author should break out of his mold once in a while, push beyond his comfort zone, even if it’s only an exercise and he doesn’t intend to publish it. Maybe even one of those zombie-distopia-shifter-romance things.