unnecessary usb protection?
I think it's necessary; what if a lot of current gets supplied, or what if a drastic temperature change causes the IV characteristics of the computer supplying the current to the USB changes? 

ONE THING TO WORRY ABOUT: "If a polyfuse has been triggered ("blown"), its resistance can increase so much (and for several days) that even 4.5 volt isn't reached, and the keyboard only gets say 3.5 Volt. The device will likely fail, by e.g., start repeating keys, etc."

"With the USB polyfuses something special is going on, because these are designed to "blow" very quickly, with just a few 100mA. Because they blow with very low currents does not mean they need less energy (heat) to blow."

Source: https://elinux.org/Polyfuses_explained