I have just read an interesting website regarding High Speed Sync (HSS) but, I did not bookmark the site so I cannot find it again. The website states that when you switch to HSS, you immediately reduce your flash intensity by half (or one stop) and then for each doubling of shutter speed, you are reducing the intensity by half again. However, when you double your shutter speed, you will also either open up your aperture one stop or increase the ISO the equivalent of a stop.
Therefore, except for the original stop lost, the flash intensity diminishes at the same rate as the f/stop is increased or the ISO doubled. This effectively means no loss from choosing HSS other than the initial stop.
The premise of the website is that the loss of flash intensity is one stop for each doubling of shutter speed. I have to find my flash manuals to ascertain if the reduction of intensity is as the website states. I cannot find any information on the Internet that qualtifies the loss of flash intensity by shutter speed selected. Can anyone either confirm the website's calculations or debunk it?
The website also recommends keeping your flash on HSS (except in certain situations) because when you are shooting at sync speed or slower, the flash will automatically switch from HSS to standard sync. So, using HSS, you have an unbroken capability to shoot at virtually any shutter speed you need without worrying that the speed is too fast. This doesn't seem like a bad idea except for certain instances like shooting with second curtain flash. Obviously it would be a moot point when shooting with studio strobes because you would not have the hotshoe flash attached to the camera and since the HSS is selected at the flash; it would not be selected with no flash attached.