Like many people I have used HDR or purely ambient light for property photography for years, when time permitted I would use a a flash or 2 to add some light to the rooms but the results were always a little bit garish, bright and weird shadows would get in the way.

Flash and Ambient light combined

This relatively novel technique is where are you capture all the ambient shots you would normally get for an HDR and also so use some very powerful bounced flash light to 2 to create that flash image of the room as well.

I would recommend you do as many flashes as as you see fit whilst travelling around the room because the more you have to play with in Photoshop later the better the results can be