I guess he might have meant "what happens if I plug it into a standard USB 3 port?  Will it hash at a lower rate with lower current, or will it not work at all?"

With possible follow-up question "what if I plug it into a USB charging port on my computer?" (the answer to that, depending on the above, being "check the maximum current it can deliver, it might be noted near the port itself or you should be able to find it in your computer's documentation/motherboard manufacturer's website)

There has been a possibility to manually set the (minimum) difficulty (UserDiff) of the shares sent to the pool. It has been replaced by (automatic) VarDiff some time ago.
This is something different than the network difficulty.