Visibility of course! Along with being a licensed firearm dealer, I also do mapping flights using a drone. This usually requires me to go out to an area that either has or can have heavy equipment in the area (construction site, aggregate pit, etc). I am usually required to have on the required safety equipment (i.e. reflective vest, hard hat and closed toe shoes). While performing the flight, I am in close proximity to the truck so if it is highly visible, than *I* am highly visible. ;-)
The PPV is perfect for this since the auxiliary battery will power all the lights for the time of the flight (20 minutes to a couple of hours) without worrying that the main battery won't start the vehicle when finished.
Plus it is saving putting the miles (15 - 250) on my other vehicle (2006 Ford Expedition w/182,000 mi) and it was relatively cheap at auction and ALL expenses can be tax write-offs since it is used strictly for business purposes.
EDIT: I forgot to mention that an added benefit is that people tend to be more cautious when around me on the road. They will usually slow down, pass carefully etc... Not sure why that is but it doesn't bother me a bit!