Lets get this straight, we are still sanding floors, and the sanding and saw dust can either be left to blow into your home, getting all over everything, or it can be contained thru dustless technology.
Dustless technology is nothing more than effective collection systems that captures the sawdust generated from sanding, and contains it in a disposal system to remove it and keep it from blowing wildly thru your house. To explain further, the sanders that we use are engineered to a vacuum system and into bags or disposal tanks, so we minimize the sawdust. There are a variety of styles, but most all offending sanders have this.
When you are working with a competent professional company they will have invested extensively in this technology, which increases their cost to do business. The benefit to you, along with routine vacuuming and tacking, you will have a cleaner floor and cleaner surfaces, and cleaner air space within your home.
If this is important to you, you should insist on only hiring a hardwood floor refinisher who uses this technology.