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The first limitation to be aware of is that you lose about one stop of flash power when you switch to high speed sync. This is usually a small price to pay for the advantages of high shutter speed and/or wide-open aperture.
In addition, if you look at the output power charts in the flash manual, you'll see that for every stop increase in shutter speed, you lose another stop of flash power. Some people incorrectly conclude from this that the flash output is so small at high shutter speeds that it must be useless. That's a mistake.