Its meant more for freezing action than overpowering the sun
Actually it's exactly the opposite.
When shooting in poor light, the flash becomes the primary source of light. In such circumstances, it's the flash which "freezes action" as, even with a relatively slow shutter speed, the subject is only lit by the flash for a much shorter period.
Ignoring HSS for a second, "standard" flash is limited to the X-Sync speed of the body being used. This speed is the fastest shutter speed at which the shutter curtains don't "overlap". In a modern shutter, it doesn't "open" then "close" a split second later, but rather one "curtain" moves across the sensor, exposing it to the light, then a second curtain follows it across very closely, covering it up again.
At speeds below X-Sync, the first curtain will completely expose the sensor before the second starts to cover it again. During the period in between, the sensor is fully exposed and the flash will fire. At speeds above X-Sync, the second curtain will start to cover the sensor before the first has finished exposing it. The gap between the curtains will get smaller as the shutter speed gets faster, and you effectively have a "slit" moving across the face of the sensor.
This normally doesn't matter as the whole sensor is exposed to the light for the same amount of time, but when using flash it becomes a problem, as when the flash fires, only the part of the sensor which is exposed by the slit between the two curtains would be exposed.
What's needed is for the flash to be lit for much longer, long enough for both curtains to move across the entire sensor so the whole sensor benefits from the flash. A flash can't just be turned on for this long though as it would burn out, so HSS is used. What this does is pulse the flash extremely quickly. The upside is that it can be on for longer and thus you can use higher shutter speeds, but the downside is you lose some power.
HSS is generally used for fill flash outdoors where the flash is not the primary light source. On a bright day, and especially with a wide aperture, you're going to need a high shutter speed to expose properly and thus you need HSS in order to use the flash at all. Whether this is of importance to you depends on whether you're going to use it this way. I tend to use fill flash quite a lot when shooting weddings, but with the flash exposure compensation down at around -1 stop so it just lifts some of the facial features or shadows from noses, hats etc in harsh sunlight.
HTH
