IMHO...height is usually an advantage/disadvantage only when you and your bike are mis-matched one way or the other. If you're too short for the bike, then you better not ever get stuck or start to tip over, you're going to struggle. If you're too tall for your steed, then god help you and your bashed in kneecaps. It's worth the time, effort and $$ to get a decent ride height out of your bike to fit your in-seam. While riding, a generous in-seam is helpful for getting your weight back and the range of motion in your knees is additive to the bike's suspension travel. As mentioned previously, strength, balance and riding ability all play a huge part in this slippery question. Anyone remember seeing little Mike Alessi piloting a KTM 525 (rather successfully) a few years ago? Because of all the crazy obstacles and situations you can get into, I think being too short can become more of an issue in the woods than on a track.