This is definitely necessary if Windows/Mac/Linux doesn't recognize the dongle at all, but also if it cannot start Bluetooth, giving you an error message such as Error 10 ( STATUS_DEVICE_POWER_FAILURE). This means you should check whether the dongle is at least looking functional. Your Bluetooth stick might be broken or at least dusty. Long story short, check the color of the dongle, and then insert it into the slot with the matching color. This difference does not mean a Bluetooth dongle will not function for sure, since bi-directional only means being able to send and receive data simultaneously, but it can, and sometimes will, cause problems. The difference in Communication may lead to problems, because USB 2 is unidirectional (half-duplex), while USB 3 is bi-directional (full-duplex).

The important differences are visuals (Because they are the only way of determining which is which) and Communication.

The functional differences are speed, communication, power consumption, cable length, capacity, price and some more. For those who don't, here is the short explanation of the visual and functional differences: The visual difference is the color of the block, blue for USB 2, and black for USB 3. Since USB 2 and USB 3 are pretty similar looking, you might not notice the difference between the two.

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