A recent Apple support note tells a tale: depending upon the particular USB setup, the placement of USB hubs, and how the keyboard and mouse are connected to the system, users may experience "unexpected behaviors" and "general system instability."
Some third-party USB hubs and devices connected though them may disconnect unexpectedly after the computer is woken from sleep. This may cause unexpected behaviors such as general system instability within open applications, or data loss if a connected device was being used to store data from an open document. If a printer was connected through the third-party USB hub, it may not be recognized.
There are a number of variables in the issue that described in the note. And Apple says it can't provide a list of the problem hubs.
To avoid the problem, the note suggests the following:
1. Connect all USB input devices, such as mice and keyboards, directly to a USB port on the computer or to an Apple display that is connected directly to a USB port on the computer. 2. Press the power button on the computer to wake it up instead of using an input device that is connected to a third-party USB hub. 3. Connect USB storage devices directly to a USB port on the computer to prevent third-party USB hubs from affecting them.
Now, suggestion Number 1 sounds like a good tip anyway. And Number 2 seems superfluous if you follow Number 1. Then there's Number 3.
What is a "USB storage device?" Certainly, the note is talking about flash drives. But what about cameras? iOS devices? Audio recorders?
No idea. Perhaps clarification will follow.