The idea is to help gadget makers have their USB devices work on any platform without having to write drivers and SDKs native to each platform.
The engineers acknowledge there have been published attacks that have reprogrammed USB devices to maliciously target a computer they are connected to. To deal with this risk, they suggest limiting connections to a set of approved sites.
To address the possibility of USB devices leaking information that could be used to breach a person's privacy, they also suggest prompting the user to authorize a site to search for the presence of a device and connect to it.
One example where they consider WebUSB might be useful is in supporting 3D printers, allowing manufacturers to build the device setup into their website.
The engineers note that it is only a draft of a potential specification and that it does not represent support from any standards group.