==Maximum useful distance== 
 I removed a section describing "special extender cables" that clearly referenced UNPOWERED 1 port hubs used as repeaters.  This section was restored saying "please look at the spec section 7.1.19.1" First, that link to the spec is obsolete as it is in the USB 2 spec.  The USB spec is at version 3.  Second, the section is about signal propagation, not power.  The illustration shows a 5 hub layout.  Those hubs would be required to be POWERED hubs.  The rule of thumb is "You can't connect a bus powered hub to a bus powered hub".  A bus powered hub plugged into a bus powered hub would work, but only the hub function would work, no downstream ports would be powered. A bus powered hub can only provide one unit load of power to a downstream port, if you connected five bus powered hubs in a row, you would run out of power on the second hub. 

 The reality is that these extender cables falsely report as self-powered hubs (which violates the spec).  A self-powered hub can provide 5 unit loads to any port.  This allows these extender cables, 5 of them in a row, to keep being powered even though all power is coming from the bus.  These devices violate the spec, and so does the layout described in this section of the article.