Sometimes the simple ideas are the best or most useful. The USB VBlock is a USB adaptor that allows you to connect or disconnect the power rails while maintaining the data line connectivity.
There are numerous situations where this might be useful. It can be used in situations where a device might be at risk of drawing too much power from your computer or where there is a potential for power to flow back from the attached device accidentally. I can think of a couple of 3D printers in my collection that, when un-powered, if you move the axis the screen flashes with the back rush of current from the stepper motors. The project creator mentions that they had a printer where the printer screen would always stay active, drawing power from the computer USB, when when the printer was powered off. A similar use case would be a GRBL-controlled CNC machine where the machine axis steppers and spindles are on a higher voltage supply which can be switched off, but the USB supply to the GRBL board remains powered. Of course, you could just unplug it but having this switchable USB adaptor is an elegant solution.
Another aspect is that you may have a microcontroller project running on a separate power supply but you still require data connectivity over USB for serial or other monitoring. Having this gadget in your collection gives you more options, and could come in handy for many different projects! The USB VBlock is supplied fully assembled and covered with some heat shrink. In the image above a case has been added using a design that is available for you to download and print over on Printables.