They explicitly went into the advantages over cameras:

• Any light condition (of course IR lighting with IR cameras are the gold standard so this can argueably be met otherwise)
• The ability to cover multiple rooms through walls with a device. A sub-10 GHz signal can penetrate most interior walls. People could be tracked without even being able to see a camera and by extension not knowing where to mess with to defeat surveillance.

So perhaps a building takes a picture of everyone as they come in the front door and also establishes a ‘WhoFi’ profile for that person. They could keep track of their movement through the building while maintaining an actionable correlation to a photo.