The only thing that doesn't work is hibernation mode, and you'd only notice that if the system ran out of battery while sleeping.
It works like this: When the system goes to sleep, it writes the entire contents of RAM into the hibernation file. Then, it sleeps. It uses a tiny amount of battery while sleeping. But as long as there is still battery left, it will wake from sleep normally, without ever using the hibernation file. Only when the battery runs out completely, the system will shut off (you'll notice the blinking sleep light is off). Then, when you restart, it will use the hibernation file to get back to where you left off.
It's only the last part, loading the hibernation file when the system shut off, that doesn't work with the SSD in the optibay.
Very useful info. Thanks.