Not at all. For example, if you already know the HSK1, feel free to start directly on the World 2. Each world = one HSK for now, and you can learn up to HSK 5 with the current application (HSK 6 on the way).
In case you stop in the middle of HSK 1, going through the stage should be very easy. I still think you should give it a try, as even if you know the word, you'll also make sentence and learn to talk (or listen if you don't like to talk). Review are only for words right now, and if you know them, they won't bother you a lot ^^
Let me know if you need any help!