Try to imagine situation you are working remotely with some USB device, connected to PC far away from home and suddenly this USB device (web-cam, printer, USB HDD) stops responding.
The one solution is to take hat and take a walk to unplug/plug USB cable for this USB device.
The second solution - is to use "USB Re-Power" utility to reset power for USB device (same as you unplug/plug USB cable).
Even if you have pressed "Safe detach USB device" for wrong device - you still can use "USB Re-Power" to reconnect it again without unplugging cable
OS: Win2K, WinXP, Vista. Sources: D6 (e-mail me to convert to other language)